WORLD METEOROLOGICAL ORGANIZATION

TECHNICALTECHNICAL NOTE NOTE No. No. 19 2

METHODS OBSERVATIONALOF OABSERVATION AT SEA CHARACTERISTICS OF THE JET STREAM PART I – SEA SURFACE TEMPERATURE A Survey of the Literature (Report prepared by a working group of the Commission for Aerology)

WMO-No.WMO-No. 71. 26. TP. TP. 27 8

Secretariat of the World Meteorological Organization – Geneva – Switzerland WMO TECHNICAL NOTES

A new series of WiVIO Publications to include a selection of papers prepared for WMO meetings and reports by the WMO Secretariat.

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No. 1 Artificial i.nducement of precipitation (out of print) Sw. Fr. 1.- No. 2 Methods of observation at sea Part I: Sea surface temperature...... Sw. Fr. 1.~ Part II: Air teluperature and. humidity, atmospheric pres­ sure, cloud height, -wind, rainfall and visibility. Sw. Fr. 1.- No. 3 Meteorological aspects of aircraft icing Sw. Fr. 1.­ No. 4 Energy from the wiml...... Sw. Fr. 10.-

No. 5 Diverses expeTiences de comparaison de radiosondes. Dr. L. M. Malet ., . ) S•. ,., 1.- and No. 6 Diagl'ammcs aerologiqucs. Dr. P. Defrise

No. 7 Reduction of atlnosphCTic pressure (Preliminary report on problems involved) ...... Sw. Fr. 3.- No. 8 Atmospheric radiation (Current i~~es~i~at~o~cs a~d. blems). Dr. W. L. Godson ... . p.ro: IJ Sw. Fr. 1.- and No. 9 Tropical ci.l'culation patterns. Dr. H. Flohn

No. 10 The forecasting from weather data of potato bligbt and other plant diseases and pests. P. lVI. Austin Bourke. and Sw. Fr. 2.~ No. 11 The standardization of the measurement of evaporation as a cliJnatic factor. G. W. Robertson No. 12 Atmospherics techniques. Sw. Fr. 3.- No. 13 A-rtificial control of clouds and hydTometeors. L. Dufour· Ferguson Hall· F.H. Ludlam, Chairman· E.J. Smith. Sw. Fr. 3.- No. 14 I-r~mogeneite du Tcseau europeen de radiosondages. ]. Lugeon ~ P. Ackermann. No. 15 The relative accuracy of rawins and contour-measured 4.- winds in relation to pCl'fol'lnance criteria. W. L. Godson 1,." No. 16 Supcradiabatic lapse rate in the upper air. W. L. Godson. No. 17 Notes onthe problems ofcargo ventilation. \V.F. lYlcDonald Sw. Fr. 3.- No.18 Aviation aspects of luountain ·waves. ill. A. Alaka ... Sw. Fr. 7.- WORLD METEOROLOGICAL ORGANIZATION

TECHNICAL NOTE No. 19

OBSERVATIONAL CHARACTERISTICS OF THE JET STREAM A Survey of the Literature

Report of a working group of the Commission for Aerology prepared by R. BERGGREN - W. J. GIBBS - C.W. NEWTON, Chairman

PRICE: Sw. fro 9.-

I WlVIO· No. 71. TP. 27 I

Secretariat of the World l\rleteorological Organization .. Geneva .. Switzerland 1958

OBSERVATIONAL CHARACTERISTICS OF THE JET STREAM

TABLE OF CONTENTS

Foreword Summary (French, Russian, Spanish) 1. Introduction 1

2. General character of wind and temperature fields ..... 3

3. Mean circulation and climatology of the jet streams 4 Treatment of data...... 5 Availability of data 0...... 6 The existing knowledge 6

4. Relation of jet stream to synoptic systems...... 11 Extratropical jet streams; large scale features .: 12 Smaller-scale features; relation to cyclones and surface frontal systems 13 Relation of jet streams to deep tropospheric frontal layers 15

5. Horizontal profiles through the jet stream I wind shear and vorticity distribution ... 17 Profiles from aerological analyses 17 Magnitudes of shear and vorticity 18 Multiple jets...... 19 Jet-stream profiles from aircraft reconnaissance...... 20 Wind shear and vorticity values revealed by aircraft flights 23

6. Variation of wind in the verticaL...... 24 Relation between jet axis and tropopause height .. . 24 Character of vertical wind profile . 24 Low tropospheric and high stratospheric wind maxima . 26 Details in the vertical wind profile; accuracy of wind soundings...... 26 Maximum observed wind speeds . . 28

7. Clear air turbulence and the jet stream . 28 IV TABLE OF OONTENTS

Page

8. Clouds and the jet stream ...... 33

9. Navigational aspects of the jet stream . 36

Figures . . 41

Bibliography . . .. 63 FOREWORD

At its fifth session, the Executive Committee of the World Meteorolo­ gical Organization approved a recommendation by the first session of the Com­ mission for Aeronautical Meteorology of WMO, held simultaneously with the fourth session of the Meteorology Division of the International Civil Avia­ tion Organization (Montreal, 1954), that a descriptive survey of existing literature on the jet stream should be issued by WMO.

In implementation of the above recommendation, the President of the WMO Commission for Aerology established, with the approval of his commission, a working group to prepare the requested survey. At its second session (Paris, 1957), the Commission for Aerology noted with satisfaction a first draft of the report and recommended early publication of the report by WMO. This re­ commendation was endorsed by the ninth session of the Executive Committee. The final report of the working group is .reproduced in the present Technical Note.

I take this opportunity of expressing deep appreciation to the members of the working group for the time and effort which they have devoted in the preparation of this report.

(D.A. Davies) Secretary-General CARACTERISTIQUES DU JET STREAM REVELEES PAR L'OBSERVATION

Le present rapport a pour but de resumer les principales caracteristi­ ques connues du jet stream, telles que nous les revelent l'observation directe et l'analyse aerologique. II n'entre pas dans Ie cadre de ce rapport d'exami­ ner les theories relatives a la formation du jet stream au les hypotheses rap­ prochant les caracteristiques du jet stream du developpement de systemes me­ teorologiques. Une longue bibliographie enumere toutefois des ouvrages qui traitent de ces questions. La premiere et la deuxieme sections portent sur des definitions, un bref resume historique et les caracteristiques generales des champs du vent et de la temperature au voisinage du jet stream, telles qu'elles ressortent des analyses aerologiques. Dans la troisieme section, un examen des problemes relatifs aux don­ nees et aux analyses est suivi d'un resume general des connaissances actuelles sur la distribution des jet streams a llechelle planetaire. Les jets d'est d'une vitesse atteignant jusqu'a 100 noeuds se trouvent dans les regions equa­ toriales au-dessus du niveau de 200 mb. Les jet streams sUbtropicaux d'ouest se situent pres de 200 mb dans les deux hemispheres, avec des vitesses typi­ ques de 100 a 200 noeuds pres des latitudes de 300 N et S. Ces jet streams ont une grande stabilite surtout en hiver; en ete, ils se dirigent vers Ie pole et s'attenuent (il devient difficile de les identifier dans l'hemisphere nord en ete). Pres de 300 mb, entre les latitudes de 40° et 60°, se trouvent des jet streams associes a la zone du front polaire; leur position est tres va­ riable et ils n'apparaissent pas distinctement sur les cartes des valeurs moyennes. Dans l'hemisphere nord, les vents moyens d'hiver les plus forts sont situes aux endroits au les thalwegs, dans les vents d'ouest des latitu­ des moyennes, penetrent dans les latitudes du jet stream sUbtropical, ces en­ droits se trouvant pres des cotes orientales de l'Asie et de l'Amerique du Nord et au-dessus du Moyen-Orient. C'est dans les regions subpolaires que se trouvent les jets stratospheriques ayant leurs plus fortes vitesses a 30 km au a des niveaux plus eleves; ce sont de forts vents drouest en hiver qui de­ viennent des vents d'est moderes en ete. La quatrieme section resume les relations existant entre les jet streams et les systemes synoptiques. Les jets sUbtropicaux, aux latitudes des hautes pressions sUbtropicales, ne sont pas lies a des systemes frontaux. Les cyclones frontaux des latitudes moyennes sont lies aux jets du front polaire d'une fagon generale, et l'on trouve dans Ie jet stream des andes et des va­ riations longitudinales de la vitesse qui sont purement liees a des systemes migratoires en surface. Le jet du front polaire est toutefois frequemment ca­ racterise par des ruptures,et dans certains cas ses relations avec les fronts RESUME VII en surface sont tres complexes. Les fronts marques sletendant jusqu'au niveau de la tropopause ont toujours des jet streams qui leur sont associes (tendant a se trouver au-dessus du front polaire, situe au niveau de 500 mb), mais des fronts facilement identifiables sont souvent absents pres des jet streams. La cinquieme section resume les connaissances sur la variation horizon­ tale du vent. Les analyses aerologiques et certaines mesures effectuees a bord d'aeronefs confirment Ie fait que sur la face anticyclonique du jet stream Ie gradient horizontal est limite par ill condition que la rotationnelle absolue ne devienne pas inferieure a zero. Pour un courant rectiligne aux la­ titudes moyennes, cela signifie que Ie gradient anticyclonique ne depasse pas une valeur voisine de 10 m/sec sur 100 km, correspondant a la valeur du para­ metre de Coriolis, mais qu1il s'en approche frequemment. Sur la face cycloni­ que, des gradients d'une valeur double ou triple sont courants et l'on a par­ fois observe des gradients cinq ou six fois plus grands. On estime que les preuves de variations marquees a une petite echelle, basees sur des donnees obtenues au cours de vols de reconnaissance, ne sont pas assez determinantes; les ecarts d'une distribution "reguliere" de la vitesse paraissent atteindre un maximum vers 10 noeuds. Des jet streams multiples, chacun ayant une lar­ geur caracteristique d'environ 500 km, peuvent toutefois se trouver tres pres les uns des autres. La sixieme section a trait a la variation du vent dans la verticale. En moyenne, les vents les plus forts ont tendance a se trouver a environ 1 km au-dessous du niveau de la tropopause; cette relation n'est pas claire tout pres de l'axe du jet stream qui est generalement situe dans la zone d'une "rupture" entre des systemes de tropopause. Des etudes statistiques montrent qu'en moyenne Ie gradient vertical aux latitudes moyennes a tendance a peu varier avec l'altitude et la vitesse du vent diminue jusqu'a la moitie envi­ ron de sa valeur maximum aux niveaux situes a 5 km de part et d'autre du ni­ veau du vent maximum. A travers des fronts distincts, Ie gradient vertical est souvent de 15 a 20 m/sec par km. Dans Ie jet stream subtropical, les forts vents peuvent ne se trouver que dans une couche peu epaisse de 100 mb de part et d'autre du niveau du vent maximum. Les problemes de la mesure du vent sont examines dans cette section ou il est dit, en conclusion, que de tres grandes et irregulieres variations de la vitesse du vent dans la verticale sont sou­ vent fictives. La septieme section du rapport resume les connaissances sur la turbu­ lence en air clair. Cette turbulence est observee presque entierement sur la face cyclonique du jet stream et elle est couramment observee avec une stabi­ lite verticale marquee. Certains indices laissent entendre que l'intensite de la turbulence dans une situation donnee varie avec la direction de vol d'un aeronef. La huitieme section examine certains types de nuages des niveaux moyens et eleves qui sont caracteristiques du jet stream. La ffieme section traite des resultats d1etudes statistiques de types de nuages, en rapport avec divers emplacements autour du jet stream. La neuvieme section donne un bref resume des methodes pratiques de na­ vigation aeronautique tirant profit du jet stream. Les previsions du vent ont VIII RESUME ete utilisees efficacement, notamment par les aeronefs qui utilisent les tech­ niques d'observation de la temperature pendant Ie vol, dans les regions ou les jet streams sont generalement associes a des fronts polaires. Le rapport se termine par une bibliographie de plusieurs centaines d'ouvrages, traitant directement ou indirectement du jet stream. HAB~~AEMNE XAPAKTEPMCTMEH CTPYWHOrO TE~HMa

B HaCTO~em CTaTbe ~enaeTCH rrOITbTIKa CYMMHpOBaTb OCHOBBble HSBeCTHble XapaKTepHCTHKH CTpyllHOrO Te~eHHH B TaKOm CTerreHH, B KaKOm 3TO rrOSBonHIDT HerrOCpe~CTBeHHble Haonm~eHHH H a3po~orH~eCKHm aHanHs.GTaTbH, O~HaKO, He ~enaeT HHKaKliX llOITbITOK HH ooc~aTb TeopHH oopaSOBaHHH CTpyllHbrr Te~eHHm HH CTpOHTb KaKHe-~Hoo rlillOTe­ SN OTHOCHTe~bHO BnHHHHH cTpymHbrr Te~eHHm Ha paSBHTHe YC~OBHm llO­ rO~I.B 3Tom CTaTbe, TeM He MeHee, ~aeTCH llO~POOHaH oTIo~OrpaWHH. BKITID~aro~aH paoOThl H llO 3THM BOrrpOCaM. B rrepBOM H BTOpOM pas~enax rrpliBO~HTCH orrpe~e~eHHR, KpaTKHm HCTopH~eCKHm OOSop, a Ta~e oo~e CBe~eHHH 0 BeTpOBhrr H TeMllepa­ TypHbrr rronRX B Herrocpe~CTBeHHom O~SOCTH OT CTpyllHOrO Te~eHTIH, KaK 3TO nOKaShrnaeT a3ponorH~eCKHm aHanTIS. TpeTHm pas~e~ paCCMaTpliBaeT rrpooneMy rro~~eHHH ~aHHhrr H npo­ o~eMY npOTISBO~CTBa aHanHsa, sa KOTOphWH cne~yeT oo~m OOSop HMeID­ ~XCH CBe~eHHM 0 n~aHeTapHOM pacnpe~eneHTITI CTpyllHhrr Te~eHTIm. Boc­ TO~Hhle CTpyllHhle Te~eHHR co CKOpOCTHMH ~o 100 ysnoB BCTpe~aroTcH B 3KBaTOpHaITbHhrr pamoHax Ha ypOBHe Bhme 200 Mo.3arr~Hhle cyoTponH~ec­ Klie CTpyllHble Te~eHTIH, BCTpe~aro~ecH B OOOHX rronymapTIRX BO~SH 200 0 MO. ypOBHH H He~aITeKO OT 30 ceBepHom H ~Hom illllpOT HMeIDT xapaR­ TepHNe CKOpOCTH 100-200 ysnoB. 3TH Te~eHHH OTnTI~aroTcH oO~bmom YC- TOM~TIBOCTbID ocooeHHO B SHMHee BpeMH, a neTOM - CBOHM C~BTIrOM B HanpaBneHliH rronmca H ocnaOneHTIeM ( neTOM liX CTaHOBHTCH TPY~HO 00­ Hap~Tb B ceBepHOM llo~ymaplili ). BonHsli 30 MO. rrOBepXHOCTH Me~y 0 0 illHpOTaMTI 40 TI 60 oOHap~liBaroTcR CTpyllHhle Te~eHHH, CBHsaHHhle C nOnRpHOM WPOHTaITbHOm sOHom H, KOTopNe o~eHb ~aCTO MeHHIDT CBoe rro­ no~eHHe li He MoryT ONTb HCHO HaHeceBbI Ha KapTN Cpe~HTIX SHa~eHliM. GaMble CHnbHNe cpe~HHe 3HMHHe BeTpN B ceBepHOM llonymaplili Haonm~~ IDTCH TaM, r~e BeTpN sarr~Horo rrOHca B cpe~HeM illllpOTe, OTKnOHHHCb rrpoHliKaroT B illllpOTN CYOTpOITli~eCKOro CTpyllHOrO Te~eHliH. TaKliMli Mec­ TaMli HB~HIDTCH BOCTO~Hoe nooepe~be ASHli H CeBepHom AMepliKH,a TaR­ ~e Gpe~Hlim BocTOK. GTpyllHhle Te~eHliH cTpaTocwepN C Halioo~ee Clinb­ HhWH BeTpaMH Ha BNCOTe 30 KM. li Bhme Haonm~aroTcH B cyorronHpHhrr pamoHax li BapbHpyroTCH OT CHnbHhrr sarr~Hhrr SHMOM ~o cpe~HflX BOC ­ TO~Hhrr ~eTOM.

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CARACTERISTICAS OBSERVADAS DE LAS CORRIENTES DE CHORRO

Resumen

El objeto de este trabajo es presentar un resumen de las principales caracteristlcas conocidas de las corrientes de chorro, tal como se ponen de 'manifiesto por la observaci6n directa y aparecen en los an~lisis aero16gicos. En,el no se intenta disentir las teorfas sobre la formaci6n de corrientes de ohorro, ni las hip6tesis sobre las relaciones entre las caracterfsticas de las corrientes de chorro y la formaci6n y desarrollo de situaciones meteoro­ l6gicas. Sin 'embargo, la bibliograffa que completa la publicaci6n contiene referenciasa trabajos que tratan de estas materias. En las dos primeras secciones se dan las definiciones y un breve resu­ men hist6rico asf c,omo las c,aracterfsticas generales de los campos de viento y temperatura en las proximidades de las corrientes de chorro puestas de mani­ 'fiesto en los an~lisis aero16gicos. Despues de examinar los problemas relativos a los datos de observaci6n y a los metodos de an~lisis, en la tercera secci6n se da un resumen general de los conocimientos actuales sobre la distribuci6n global de las corrientes de ohorro. En las regiones ecuatoriales se forman corrientes de chorro del Este, con velocidades de hasta unos 100 nudos, por encima del nivel de 200 mb. En las regiones subtropicales de los dos hemisferios se encuentran corrientes de chorro del Oeste en la proximidad del nivel de 200 mb, con velocidades tf­ picas de 100 a 200 nudos, alrededor de 30° Norte y Sur. Estas corrientes son muy estacionarias, sobre todo en invierno, desvi~ndose hacia el polo y debili­ t~ndose en verano (en esta epoca del ano es muy diffcil identificarlas en el hemisferio Norte). Entre los 40° y 60° de latitud, y hacia el nivel de 300 mb, hay corrientes de chorro asociadas con la zona del frente polar, que son muy variables en posici6n y no aparecen claramente en los mapas de valores medios. Los vientos medios m~s fuertes se presentan, en el hemisferio Norte, en los sitios en donde los collados de presi6n de la circulaci6n del Oeste en las la­ titudes medias penetran en la zona de las corrientes de chorro subtropicales; esos lugares se hallan en las proximidades de las costas orientales de Asia y de America del Norte y sobre el Oriente Medio. En las zonas subpolares se en­ cuentran corrientes de chorro estratosfericas, con vientos m~ximos a alturas de 30 km y m~s, los cuales varian de fuertes corrientes del Oeste en invierno a corrientes moderadas del Este en verano. La cuarta secci6n contiene un resumen de los conocimientos sobre las relaciones, las corrientes de ohorro y las situaciones sin6pticas. En el cin­ tur6n subtropical de altas presiones las corrientes de chorro no aparecen re­ lacionadas a sistemas frontales. De una manera general, las depresiones fron­ tales de las latitudes medias est~n relacionadas can las corrientes de chorro del frente polar, y se han encontrado en estas corrientes ondulaciones y RESUMEN XIII variaciones longitudinales de velocidad asociadas con sist,emas superficiales migratorios. Las corrientes de chorro del frente polar presentan frecuentemente discontinuidades, y en ciertos casos su relaci6n con los frentes en superficie es muy compleja. Los frentes muy marcados y que alcanzan hasta el nivel de la tropopausa van siempre acompafiados de corrientes de chorro (generalmente situa­ do's por encima del nivel de 500 mb en la zona del frente polar) perc no es fre­ cuente que en las proximidades de las corrientes de chorro existan frentes f~­ cilmente identificables. La quinta secci6n contiene un resumen de los conocimientos sobre la va­ riaci6n horizontal del viento. Los an~lisis aero16gicos y ciertas medidas efec­ tuadas desde avi6n han puesto de manifiesto que en la parte anticic16nica de las corrientes de chorro el gradiente del campo de viento est~ limitado por la condici6n que la vorticidad absoluta no puede ser menor que cero. En el caso de corrientes rectilfneas, en las latitudes medias, esta condici6n significa que el gradiente anticic16nico no excede, perc frecuentemente se aproxima, de un valor del orden de 10 m/sec en 100 km, que corresponde al valor del para­ metro de Coriolfs. En la parte cic16nica, gradientes dobles 0 triples que ese valor son frecuentes, y a veces se han observado gradientes cinco 0 seis veces mayores. Se consideran como poco concluyentes las pruebas de variaciones mar­ cadas en pequefia escala, basadas en observaciones efectuadas durante vuelos de reconocimiento; las desviaciones de un "perfil regular" del campo de velocida­ des parecen ser como m~ximo de unos 10 nudos. Sin embargo, es posible encon­ trar, muy cerca una de otra, corrientes de chorro mGltiples, cada una con su ancho caracterfstico de 500 km. La secci6n sexta est~ dedicada a la variaci6n vertical del viento. Gene­ ralmente, los vientos m~s fuertes se encuentran aproximadamente a 1 km por de­ bajo de la tropopausa; esta relaci6n no es muy clara cerca del eje de la Cor­ riente de chorro, que tiende a situarse en una "rupturatt entre tropopausas. Los estudios estadfsticos indican que, en promedio, el gradiente vertical, en las latitudes medias, varia poco con la altura y que, en promedio tambien, la velocidad disminuye casi a la mitad del m~ximo, a niveles 5 km por encima y por debajo del nivel de viento m~ximo. A traves de frentes bien definidos, e1 gradiente vertical es con frecuencia de 15 a 20 m/sec. por ki16metro. En las corrientes de chorro subtropicales los vientos muy fuertes pueden quedar com­ prendidos en un estrato poco espeso, unos 100 mb por encima y por debajo del nivel de viento m~ximo. En esta secci6n se trata tambien de los problemas que presenta la medida del viento, y se concluye que en muchos casos las varia­ ciones muy grandes e irregulares de la velocidad del viento son ficticias. En la septima secci6n se resumen los conocimientos sobre turbulencia en aire despejado. Este tipo de turbulencia se observa casi exclusivamente en el lado cic16nico de las corrientes de chorro, y muy frecuentemente cuando existe una estabilidad vertical muy marcada. Ciertas indicaciones hacen pen­ sar que la intensidad de la turbulenciaen una misma situaci6n varia con la direcci6n de vuelo del avi6n que la experimenta. Ciertos tipos caracterfsticos de nubes medias y altas asociadas a Cor­ rientes de chorro constituyen el tema de la octava secci6n, en la cual se exa­ minan los resultados de estudios estadfsticos de los tipos de nubes en relaci6n XIV RESUMEN con las diversas zonas que se distinguen en los alrededores de las corrientes de chorro. La novenay ~ltima secci6n contiene un breve resumen de los metodos pr~cticos de navegaci6n aerea para sacar ventaja de las corrientes de chorro. En las regiones en que estas corrientes est~n generalmente asociadas con fren­ tes polares, se han utilizado con buenos resultados las previsiones de viento, sobre todo para aviones que utilizan las tecnicas de observaci6n de la tempe­ ratura durante el vuelo. La publicaci6n incluye, al final, una lista de varios cientos de refe­ rencias bibliogr~ficas de trabajos que tratan directa 0 indirectamente de las corrientes de chorro. OBSERVATIONAL CHARACTERISTICS OF THE JET STREAM

1. INTRODUCTION

According to a definition recommended by the Commission for Aerology, World Meteorological Organization, "A jet stream is a strong narrow current, concentrated along a quasi-horizontal axis in the upper troposphere or in the stratosphere, characterized by strong vertical and lateral wind shears and featuring one or more velocity maxima". For operational purposes, the Com­ mission has recommended the criteria that "Normally a jet stream is thousands of kilometres in length, hundred of kilometres in width and some kilometres in depth. The vertical shear of wind is of the order 5-10 m/sec per km and the lateral shear is of the order 5 m/sec per 100 km. An arbitrary lower limit of 30 m/sec is assigned to the speed of the wind along the axis of a jet stream".* Al though the term "jet stream" was not applied to the atmospheric phenom­ enon until 1947, intimations of its existence can be found in earlier litera­ ture. For example, Dines (1911) presented composite vertical cross sections showing the distribution of temperature between high- and low-pressure cen­ ters, and indicated that strong localized winds must exist, with maximum speeds generally at the 10 to 12 km level. Pilot-balloon observations in England (Dobson, 1920) showed winds in excess of 100 mi/hr (45 m/sec) near the tropopause, verifying the existence of strong winds computed from move­ ments of cirrus clouds. The concentrated nature of the band of strong west­ erlies was indicated by mean cross sections shown by Bjerknes et al (1933) and by Willett (1944). -- Shaw (1904) computed the winds at the 4 km level from the Northern Hemi­ sphere winter mean charts prepared by Teisserenc de Bart several years earlier, and concluded that "••• the distribution of pressure at the 4000 meter level is favorable for a steady circulation of air around the polar axis, with an average velocity of 50 mph (20-25 m/sec)", the motion being in waves, and that "••• in the southern hemisphere motion follows the lines of equal lati­ tude more closely". Shaw also showed that the motion at 4 km was quite simi­ lar to the thermal wind between the earth's surface and that level. Hesselberg (1913) and Douglas (1922), using data on cirrus movements which indicated upper-level winds up to 65-75 m/sec, deduced certain features of the wind and thermal structures of cyclones which are in rather good agree­ ment with the results obtained by direct aerological analysis.

* The Executive Committee of the World Meteorological Organization adopted this definition as a provisional definition of the term "jet stream" [Res. 25 (EC-IX)] • 2 INTRODUCTION

From speculations on the thermal structure of cyclones, Goldie (1937) predicted the existence of a narrow zone of strong winds (width 500 km, speed around 60 m/sec). From composite plots of cloud movements against distance from cyclone centers, Goldie (1939) found cyclonic shear of the order 25 m/sec in 900 km, a modest value in light of later observations but at least sugges­ tive of one important feature of jet-stream structure. Analyses from the early swarm meteorograph ascents over Europe, e.g. by Bjerknes and Palmen (1937), show concentrated currents with geostrophic speeds in excess of 100 m/sec. Goldie, Shaw, Brunt, and others recognized that a fast upper current could in some way be important for explaining the deepening of ·cyclones. The references cited above suggest that the existence of a wind field, having the general character of the jet stream, was at least recognized in a qualitative way many years ago. Because of the sparsity of observations in the high troposphere and stratosphere, the implications of the early deduc­ tions and observations could not be followed up in any systematic manner, until the abrupt increase in the density and quality of the world network of aerological observations in the 1940's made possible the routine analysis of conditions in the upper levels. The first organized studies of the jet stream were carried out bya group, comprising investigators of several nationalities, at the University of Chicago in 1946-1947 under the leadership of Rossby and Palmen (Staff Members, University of Chicago, 1947; Rossby 1947; Palmen 1948b). It was immediately apparent that the jet stream, in which the major part of the kinetic energy of the hemispheric wind systems is concentrated within a small part of the total volume of the atmosphere, is a phenomenon of fundamental importance for understanding both the general circulation and the day-to-day behavior of synoptic disturbances. Aside from the theoretical implications, study of the jet stream has been spurred by the need for a detailed knowledge of the wind distribution in the upper troposphere and in the stratosphere, which arose with the advent of higher-speed, higher-altitude and longer-range aircraft. It is not surprising that a vast amount of literature connected with the jet stream has appeared in the last decade. The intention of this monograph is.to present a broad summary of present knowledge on this subject. Several summaries have appeared earlier, the most comprehensive being that by Riehl, Alaka, Jordan and Renard (1954). For the sake of completeness, it will be necessary to repeat much of the discussion found in the other summaries. An effort will be made to present different illustrative material wherever pos­ sible, a consequence being that in some cases the earliest work of a given kind may not be shown. The present monograph will be concerned only with observational features of the jet stream. Theories of the jet stream, and its implications for the forecasting of weather systems, have been dealt with in extenso by Riehl et ~ (1952, 1954). The bibliography of the present report includes papers on theory and forecasting. Because of limitations in instrumentation, or simply the incompleteness of observations, much of the data gathered on the jet stream cannot be GENERAL CHARACTER OF WIND AND TEMPERATURE FIELDS 3

regarded as completely definitive. Thus there are inevitable differences in interpretations of the data. Where justifiably conflicting viewpoints exist, an attempt will be made to present both sides. At the same time, the writers will occasionally exercise the liberty of suggesting whether, in their opin­ ions, given interpretations appear to be justified by the evidence presented. It is quite possible that some important facts about the structure and behavior of the jet stream will have escaped the attention of the group pre­ paring this report. For those interested in searching the original literature, a fairly extensive bibliography has been appended.

2. GENERAL CHARACTER OF WIND AND TEMPERATURE FIELDS

Because of the intimate relation between the fields of wind and tempera­ ture, the character of the jet stream cannot be discussed without at the same time describing the salient features of the field of temperature. The details of the wind and temperature fields vary in different situations, and no single illustration can be regarded as typical for all cases. The broad features shown in Figure 2.1, however, are fairly characteristic of the middle-latitude westerlies in winter. This is a mean cross section overNorth America for 0300 GCT 30 November 1947, using all soundings between longitudes 65° and l35°W, the averaging being performed with respect to the axis of maxi­ mum wind. The corresponding 300 mb chart is shown in Figure 2.2, in which the concentration of height contours near latitude 45° is strikingly evident. The general features shown by these figures have been discussed in detail by Staff Members, University of Chicago (1947), palmen and Collaborators (1948), Riehl (1948b), and Nyberg (1949). These are, broadly, the following: (1) In the troposphere, a zone of strong horizontal temperature gradient, usually most pronounced in a layer sloping upward toward the cold air, sepa­ rating more or less homogeneous polar and tropical air masses. The zone of strong baroclinity mayor may not be characterized by a distinct ir£n1 having pronounced vertical stability. Within the barocline zone, whose width is of the order 500-1000 km, is concentrated a substantial part of the total pole­ to-equator temperature difference. (2) In the stratosphere above the tropospheric baroc1ine zone, the hori­ zontal temperature gradient reverses, with warmest air 500-1000 km to the left (north, in this case) and cooler air to the right, at a given level. North of the warm "bubble", near latitude 55° in this figure, the stratospheric tem­ perature characteristically decreases poleward in winter, although this is not necessarily so in summer. (3) A relatively low and warm "polar tropopause, around 8 to 10 km elevation, north of the frontal zone. Some distance to the south, a high cold "tropical" tropopause at 16-17 km, characteristic of tropical air in lower latitudes. Over and just south of the frontal zone, an "extratropical" tropo­ pause at 10-12 km, with a characteristic upward bulge near the 200 mb level. 4 MEAN CIRCULATION AND CLIMATOLOGY OF THE JET STREAMS

(4) In the tropospheric zone of strong baroclinity, a rapid increase of wind with height up to around the 250 to 300 mb level, and a decrease with height above that level, where the horizontal temperature gradient reverses. Further north and south, weather vertical shear where the baroclinity is weak. In this particular example (Figure 2.2), there was a closed low near latitude 55°-60°, with easterly winds to the north; this is naturally not character­ istic of the typical situation in all longitudes. In an average winter situa­ tion the westerly wind increases gradually with height through the troposphere in the polar air, and in the stratosphere, north of the warm "bubble" men­ tioned under (2), a more pronounced increase of westerly wind with height gen­ erally occurs. (5) The surface wind being relatively weak, the wind in the upper tropo­ sphere and lower stratosphere depends essentially upon the integrated thermal wind from the surface upward. In accord with the thermal features discussed above, a core of strongest wind or "jet stream" is observed above the baroclinic zone, and in the vicinity of the tropopause break, having maximum strength (90 m/sec in this case) at the level where there is no horizontal temperature gradient. The jet stream is flanked on the right side (Northern Hemisphere) by strong anticyclonic shear in a band perhaps 5° latitude wide, and on the left side by more pronounced cyclonic shear in a corresponding band. On the anticyclonic flaru<, the absolute vorticity is characteristically near zero in a narrow band in the upper troposphere (anticyclonic shear near the value of the Coriolis parameter; in middle latitudes around 10 m/sec in 100 km). On the cyclonic flank, the maximum absolute vorticity is for a well-marked jet ordinarily in excess of two up to five times the Coriolis parameter. Further north and south, weaker horizontal shear is observed. There are many variations on the broad features shown in Figures 2.1 and 2.2; some of these will be discussed in the following sections. In parti­ cular, the situation illustrated ~ccurred in mid-winter, and, especially in the stratosphere of middle and high latitudes, the thermal structure undergoes strong changes between winter and summer, with consequent large seasonal varia­ tions in the character of the wind field.

3. MEAN CIRCULATION AND CLIMATOLOGY OF THE JET STREAMS

Because of the great variations of the instantaneous wind field, it is appropriate to examine the structure of the atmosphere in the mean state, before returning to the complexities of individual cases. An examination of the mean state has the further advantage that averages can be pieced together to provide a picture of the circulation in regions where observations would be too sparse to determine the circulation at a given instant of time. It should be borne in mind that the available data do not justify a rigid acceptance of the precise values of the wind field shown on mean upper air charts. Although the major features are believed to be known with fair cer­ tainty, precise numerical values can only be regarded as tentative and subject MEAN CIRCULATION AND CLIMATOLOGY OF THE JET STREAMS 5 to revision as more data become available. Treatment of Data. The utilization of data to obtain a picture of the mean circulation and climatology of the jet stream is a complex and exacting task. The data used may be upper wind observations, observations of tempera­ ture and the calculated geopotential field, or a combination of these types of data. Upper wind data are best analyzed by using the assumption of Brooks et al (1950) regarding the manner in which wind vectors are distributed. This in­ volves the frequency analysis of the west-east and south-north components of the individual wind vectors observed at regular intervals. From this analysis are obtained the vector mean and standard vector deviation for groups of ob­ servations at individual observation stations (usually, daily observations grouped by months). This type of analysis is complicated by the fact that the data for levels where jet streams occur are usually incomplete. In the case of visual upper wind observations, either cloud entry, low elevation or great distance of the balloon from the observer frequently cause termination of the observation be­ fore the jet-stream level is reached. Even with radio and radar wind-finding methods, range and elevation limitations have the same effect, though for a smaller number of cases. If the missing observations were uncorrelated with the wind speed and di­ rection, the sample frequency distribution would yield a representative vec­ tor deviation, but if some correlation does exist the frequency distribution of the sample will be biased and unrepresentative of real conditions. It is not known precisely how winds at jet-stream levels are correlated with cloudi­ ness (see later discussion on clouds and jet stream); however, it is certain that limitations of range and elevation are correlated with the wind strength at jet-stream levels so that there is a tendency for all observed wind distri­ butions at these levels to be biased toward light winds. Thus visual observa­ tions will yield distributions containing the unknown bias due to cloudiness and also a bias toward light winds, while radio and radar wind observations will suffer from the latter bias. This means that it is necessary to be ex­ tremely critical in determining vector means from wind observations when at­ tempting to establish the position and intensity of the jet stream on mean charts. The use of the mean topography of constant-pressure surfaces in determin­ ing the mean wind field depends on the accuracy of the height observations and the validity of the geostrophic assumption. A radiosonde network with com­ patibly instrumented stations 250 to 500 km apart is required, to give a mean topography of the necessary accuracy. Little is known regarding the validity of the geostrophic relationship between topography and mean winds, but it may be said to be increasingly doubtful from latitude 30° equatorwards. The use of mean temperature gradients in determining the vertical shear of mean winds also depends upon the geostrophic assumption and is therefore limited by the same considerations. 6 MEAN CIRCULATION AND CLIMATOLOGY OF THE JET STREAMS

Because of the many errors which may arise in assessing the mean circula­ tion and climatology of the jet stream, it is important. that all studies should clearly indicate the nature of the data used and the methods of ana­ lysis employed. Availability of Data. An examination of upper-air networks (see, e.g., Figure 2 in Namias and Clapp, 1951) reveals the areas where the mean winds in jet-stream levels may be established with reasonable certainty, and shows that over most oceanic areas and in equatorial regions data are not sufficient for an accurate and comprehensive picture to be drawn. It is essential to realize that all analyses that have been made of the complete global circulation de­ pend, over very large regions, upon a piecemeal combination of observations having different lengths of record and sometimes even different periods of record, together with extrapolations from available data regions (either hori­ zontally or vertically). Information useful in determining the mean circulation and climatology of the jet stream may be grouped under three main headings : (1) The large mass of observational data of upper winds, temperatures, humidities, and geopotentials of isobaric surfaces, published by some authori­ ties and available on request from others, which is too voluminous to be used without considerable collation and processing. (2) Means and frequency analyses of upper air data, such as World Weather Records published by the United States Weather Bureau and the New Zealand Meteorological Office. These publications, unfortunately, do not always in­ dicate whether the records are likely to be biased because of missing observa­ tions. (3) Published papers on mean winds, mean constant-pressure topography and mean temperature, notably that of Brooks et ~ (1950). Here again it is unfortunate that only rarely do these papers give an adequate description of the extent and reliability of the data used in their preparation. If a comprehensive and extensive study of the mean circulation and cli­ matology of the world's jet streams is to be made, a coordinated program of analysis of upper-air data must be carried out by each meteorological service. The Existing Knowledge. An examination of the literature suggests that there are five main areas of occurrenCe of jet streams (Gibbs, 1953): over eguatorial regions, in the vicinity of latitudes 30° in both north and south, and between latitudes 40° and 60° in both hemispheres. In addition, jet streams at very high levels are found over the subpolar regions. Figures 3.1 to 3.5 give in broad outline the variation of the mean zonal flow with altitude, latitude, longitude, and time of year (for spring and fall charts, see Bannon 1954, Jenkinson 1955 and Kochanski 1955). Figure 3.1 gives the variation of the flow with latitude and altitude in summeT and winter, averaged over all longitudes (see also Namias and Clapp 1949, Petterssen 1950, 1956), while in Figures 3.2 and 3.3 the variation of flow with latitude and longitude are indicated for the 200 mb level. Figure 3.4, a mean cross sec­ tion along SooW in the Northern Hemisphere, is presented to show the conditions MEAN CIRCULATION AND CLIMATOLOGY OF THE JET STREAMS 7 in a location with extensive observational data, and also to bring out the structure of the circulation in high levels. Not all the features shown in Figure 3.4 are necessarily representative of other longitudes, because of the effects of the land-sea distribution. For example, the strong subtropical maximum of easterlies shown by these sections appears to some extent to be a localized phenomenon affected by the North American continent. Figure 3.5, showing the monthly mean zonal flow, averaged over all longitudes for the 300 mb level in the Northern Hemisphere, illustrates the general nature of the seasonal variations in latitude and strength of the westerly flow during a particular six-month period. It is seen (cf. Figure 3.1) that the mean west­ wind system as a whole undergoes a marked variation, being strongest and closest to the equator in winter. The annual meridional shift is quite simi­ lar to that undergone by the subtropical high-pressure belts at sea level. Knowledge of the equatorial jet stream (high-level maximum easterlies in Figures 3.1 to 3.3) is limited to the relatively few radar or radio-wind sta­ tions in these latitudes (because of persistent cloudiness visual wind ob­ servations are rare at the appropriate levels). Radiosonde observations of temperature and geopotential at isobaric surfaces are of little assistance in determining the wind structure in equatorial and subequatorial regions because of uncertainties regarding the geostrophic assumption, and the extreme sensi­ tivity of geostrophic wind computations to the accuracy of observations in these latitudes. Cognizance of a temperature minimum at about 100 mb in low latitudes led Willett (1944) to suggest a belt of strong easterlies in subequatorial lati­ tudes in summer. Brooks et al (1950) suggested a high-level belt of stronger easterly winds in equatorial regions and Gibbs (1953) suggested that this belt might have jet-stream characteristics. In recent years, an increasing amount of evidence, admittedly still some­ what fragmentary, has been accumulating to define the character of an equa­ torial jet stream occurring above the 200 mb level with speeds sometimes ex­ ceeding 90 kt (the term equatorial as here used refers to the general region near, but not necessarily on, the equator). This jet stream has been observed over Africa, Southeast Asia, and Australia, generally within 15° latitude of the equator and apparently having a most northerly position in July and most southerly position in January (cf. Figure 3.1; also Gibbs 1953 where the easterly jet is indicated as having a mean speed of 40-45 kt at 100 mb, in a sector near 150 0 E). There is ample support for the presence of the subequatorial easterly jet in particular localities. Vuorela (1948, 1950) shows examples of easterlies of 80-100 kt in the equatorial Atlantic, and Davies and Sansom (1952) reported occasional 3- to 15-day periods of easterly winds in excess of 45 kt at 150­ 200 mb, over East Africa in summer and winter. In the Southern Asia region, Koteswaram (1956) has shown the presence of a summer easterly jet of consider­ able longitudinal extent, with core at 100-150 mb in latitude 15°N (see Fig­ ure 3.3). This is supported by Ramsey (1955), who also found a January maxi­ mum at 2°S. Hay (1953) found easterlies at Singapore (IoN) throughout the year at the 100-150 mb level, the maximum speed sometimes being greater than 8 MEAN CIRCULATIDN AND CLIMATOLOGY OF THE JET STREAMS

90 kt, with similar results at Hong Kong (22°N) during the summer months. From aircraft reports, Emery (1956) reported the existence in this region of a narrow core of strong easterlies with maximum speed 75-100 kt above 200 mb. Over India, Krishna Rao (1952) considers that easterly jet streams are most likely to occur between 5° and 18°N, at the 100-150 mb level, while over Aden (13°N) Frost (1952) and Austin (1953) have found a July maximum at 100-150 mb. In the Australasian area, Bond (1953) located jets of SO kt at Darwin (12°S) in January and February 1953. The increasing volume of upper wind data should enable more definite conclusions to be drawn in the future regarding the posi­ tion, intensity and conformation of this jet stream, but it will be necessary to make a careful statistical analysis of data, with due allowance for miss­ ing observations and for bias. The mean data, as well as individual cases analyzed by Koteswaram (1956) and others, indicate that the low-latitude easterlies are strongest and most coherent when in their most northerly position in Northern Hemisphere summer. Their steadiness is quite high at that time, in the regions south of the principal land masses; however (see Figure 3.3) in localities such as the western and central Pacific Ocean the mean easterlies are poorly developed. Here, as indicated by Riehl (1948a), the high-level circulation tends to take on the form of transient closed eddies. Riehl (1954b, p. 250) shows an ex­ ample of a localized westerly jet in the central Pacific, in latitudes l5-200 N in July, with maximum speed of more than 100 kt. Thus within the latitudes of the summer mean hemispheric easterlies, local westerly jets may be found which reach the intensity of wind maxima connected with middle-latitude frontal sys­ tems in summer. Details of the high-level wind distribution in equatorial regions are discussed at length by Palmer et £1 (1955). These authors indicate two east­ erly maxima of the mean winds (averaged around the hemispheres) throughout the year, the summer-hemisphere jet being most pronounced. The separating minimum of mean easterly wind speed near the equator is due mainly to great variability, rather than low wind speeds. A narrow and shallow thread of westerlies (mean zonal speed 10 m/sec) is found at 50 mb (20 km) right over the equator, surmounted by the easterly "Krakatoa winds" which reach a mean speed of more than 30 m/sec at 10 mb (3D km). The sUbtropical jet streams of both hemispheres have been the subject of considerable study during the last five to ten years, as evidenced by the work of Austin (1953), Bannon (1954b), Chaudhury (1950), Gabites (1952), Gibbs (1952, 1953), Gilchrist (1955), Hess (1948), Hofmeyer (1952, 1953), Hutchings (1950, 1952b), Johnson (1952), Koteswaram (1953), Krishna Rao (1952), Loewe and Radok (1950), Matsumoto, Ito~ and Arakawa (1953), Mohri (1953), Moir (1950), Mironovitch (1953), Ockenden (1939), Palmen (1951a), POrter (1952a, b), Row (1951), Sutcliffe and Bannon (1954), and Yeh (1950). The subtropical jet stream appears on mean charts at the 2DD mb level (Figures 3.2, 3.3), and on vertical sections, as the strongest and most con­ tinuous belt of westerlies, in the latitudes of the subtropical high-pressure belts at the surface (note, in Figure 3.1, that the greatest westerly speeds aloft are directly over the latitudes of zero zonal speed at the surface, both summer and winter). MEAN CIRCULATION AND CLIMATOLOGY OF THE JET STREAMS 9

The Southern Hemisphere seems less influenced by orographic effects and apparently has a more regular mean circulation than the Northern, so that ob­ servations of the subtropical jet stream from the Southern Hemisphere may be more representative of its essential character. It appears that in the Southern Hemisphere the sUbtropical jet stream occurs near the 200 mb level, at latitudes slightly below 30 0 S in winter and between 35° and 400 S in summer. The mean wind speed in the jet stream region approaches 100 kt in winter, but is generally less than 70 kt in summer. In winter the jet stream is a parti­ cularly persistent feature on 200 mb charts, the speed maximum on individual daily charts being of the order 200 kt and the alignment of the jet axis being dominantly west-east. Although it is not possible to construct reliable hemi­ spheric 200 mb charts for the whole Southern Hemisphere, it seems likely that there is not a great deal of variation of the mean subtropical jet stream with longitude. The Northern Hemisphere subtropical jet stream has been identified over the Mediterranean-Middle East-India region where it appears to have charac­ teristics similar to those described above. However, in the Western Atlantic and to some extent in the Western Pacific, it appears that the subtropical jet stream is, on mean charts, difficult to distinguish from active higher­ latitude jet streams occurring in those regions. Reports from North Africa, Bahrein, and India indicate a jet stream near 300 N with a mean speed over 100 kt at 200 mb in winter, and near 40 0 N in sum­ mer, at a lower height and with considerably lower speed. Over the Asian land mass in winter, a double stream occurs. For example, Chaudhuri (1950) found maxima at 31° and 400 N at longitude 1200 E. In the Japanese region, Ooi et al (1951-1953) found similar results. At 500 mb in the Far Eastern region, Murakami (1953) established that the jet stream was stationary in winter at about 30 0 N until May, when a secondary stream appeared at 55°N. A cross seC­ tion at 80 0 W (east coast of North America) by Hess (1948) showed a strong maximum at 35°N of 100 kt at a height of 200 mb, and a secondary maximum at a higher level at 55°N in winter; whereas in summer, the maximum speed of 50 kt at 200 mb was found at 55°N, with an indistinct secondary, not clearly sepa­ rated, near 40-45°N. The winter maximum speed may be compared with that ob­ served in a comparable region of Asia, about 150 kt (Mohri, 1953) to 180 kt (Bannon, 1954c) average near 200 mb over Southern Japan (cf. Figure 3.2). In the Hawaiian Islands region, Bannon (1954b) found that in winter there are two maxima of westerly flow at 200 mb height, one of 75 kt at 20 0 N, the other at 300 N. He identified the same pattern over the West Indies, with a maximum of 80 kt at 20-25°N and the secondary 10° or more further north. To isolate the characteristics of the subtropical jet stream, T.N. Krishna Murti (report as yet unpublished) at the University of Chicago has analyzed the low-latitude wind field of the Northern Hemisphere on a daily basis for three winter months (December 1955 through February 1956). Examples of the daily analyses are shown in Figure 3.6. When averaging is done with respect to the jet axis rather than by geographical locations, the mean jet at 200 mb stands out with great clarity. It was found that the winter subtropical jet has three waves around the hemisphere, with median locations of crests at latitudes 30-35° and troughs at latitudes 22-25°N. In agreement with the findings of Namias and Clapp (1949), large wind speed variations are observed 10 MEAN CIRCULATION AND CLIMATOLOGY OF THE JET STREAMS along the jet axis. Greatest speeds are found at the crests (compare Figure 3.2) : 140-150 kt at 70 0 W (east coast North America) and 40 0 E (Middle East), and 180 kt near 145°E (east coast Asia). Minimum speeds of 100-110 kt were found at lowest latitudes on the jet axis. It will be noted that the crests in the subtropical jet axis oCCur at the longitudes of the middle-latitude troughs on upper-level mean charts for winter. There was little deviation from the above pattern on a day-to-day basis, except for latitudinal shifts of the jet axis 7 to 8° north Or south of its median position. The greatest steadiness in location of the subtropical jet axis is found in the region from India across China through southern Japan. The small de­ gree of meridional movement here is attributed to the fact that in winter the jet hugs the south side of the Himalaya complex; the stability being favored both by its presence as a physical barrier and as a high-level cold source (see Ramage, 1952). Northward shift of the westerly subtropical jet (to a position north of the Himalayas) and replacement by the summer subequatorial easterlies occurs quite rapidly. According to Sutcliffe and Bannon (1954) and Tun Yin (1949), this shift over the Middle East-Southeast Asia region is closely tied to the onset of the summer monsoon. The secondary maximum appearing at higher latitudes, in the earlier studies mentioned above, appears to be associated with the middle latitude or "polar front" jet stream. Although such jets are quite pronounced on daily charts, they are very obscure on mean charts because of their relative transi­ ence in time and space. The charts by Brooks et al (1950) show greatest varia­ tions about a mean state in the eastern parts of the North Atlantic and North Pacific Oceans, where the mean vector deviation of the 300 mb wind in winter is 40 to 50 kt. Studies such as those by Hubert and Dagel (1955) and Murray and Johnson (1952) indicate that these jet streams are frequently closely associated with polar fronts. Because of their variation in geographical position (Phillips, 1950) they are not apparent on mean charts except in areas of persistent fron­ tal occurrence such as the eastern coasts of North America and Asia (Figures 3.2, 3.3). In these locations a high frequency of frontal occurrences gives rise to a quasi-permanent jet stream which on a mean chart appears as a parti­ cularly strong wind maximum which merges with the mean subtropical jet stream. From a section across the North Atlantic, Johnson (1953d) found the main westerly flow (for January 1950) to be centered at 61 0 N with a mean speed of 60 kt at a height below 300 mb. From consideration of three mean cross sec­ tions in the North Atlantic region in January 1952, Hubert and Dagel find a polar jet at latitudes 40-50oN and subtropical jets near 12° on the wsst side and near 25°N on the east side of the Atlantic. At the same time, a high-al­ titude jet stream circulation appears, most clearly defined over Scandinavia. There it appears as a current centered near 62°N with mean winds of 56 kt at 100 mb, still increasing with height. This latter current corresponds to the winter "polar night maximum" indi­ cated by the hydrostatically computed wind field shown by Kochanski (Figure 3.4) at 65-75°N and particularly strong above 50 mb. This feature is strikingly evident on the winter mean 41 and 96 mb charts of Scherhag (1948). RELATION OF JET STREAMS TO SYNOPTIC SYSTEMS 11

In the Southern Hemisphere, observations in middle and high latitudes are particularly deficient, but from experience with frontal analysis at the sur­ face Gibbs (1953) suggested that a minor mean jet stream may exist in higher latitudes (in summer, around 50 kt at 300 mb near latitude 60 0 S). It is well known that in winter a well marked cold pool occurs over Antarctica and ex­ tends to about 100 mb. Gibbs has suggested that this may be associated with a mean jet stream at about 100 mb between latitudes 70° and 80 0 S. This is also shown on the mean sections of Hutchings (1950) and of Flohn (1950b), who indi­ cate mean westerlies of 30 m/sec at 30 km height near the South Pole. The high-level stratospheric jets in the subpolar regions are the fea­ tures which undergo the strongest annual variation, from very strong wester­ lies in winter to moderately strong mean easterlies in summer. This variation of wind is associated with the annual temperature variation of 35-500 C at 20-30 km over the North Pole (Kochanski, 1955) and a probably greater varia­ tion over the South Pole. For an extensive discussion of the available knowledge of winds higher than 30 km (up to 100 km), the reader is referred to a survey by Murgatroyd (1957). In winter, the subtropical maximum of easterlies (Figure 3.4) appears to be strongest near 30 km height. Maximum westerlies are found near 60 km, with mean speeds in excess of 100 m/sec at latitudes 50-60°. The westerlies again decrease upward, and at least in the subtropics give way to easterlies near the 100 km level. In summer, a maximum of easterlies is observed, slop­ ing upward from 50 km in the tropics to around 80 km in subpolar regions. Maximum easterly speeds of 70 m/sec or more are found at latitudes 15-40°. The easterlies give way to westerlies near the 100 km level. The variation from winter westerlies to summer easterlies near 60 km is associated with the strong seasonal temperature variation noted in connection with Figure 3.4, and the "polar maxima" in that figure show in fact the lower extensions of the general high-level wind belts. The few illustrations in Figures 3.1 to 3.5 have been chosen to bring out the main features of the global wind patterns near jet-stream levels. It must be emphasized that there are strong regional differences in the mean flow and that hemisph€ric means (Figure 3.1) are not adequate representations for any given longitude. This is clear from Figures 3.2, 3.3 and 3.6. Examples by Radok and Grant (1957) and Kochanski (1955) demonstrate also that there are large local variations even in the seasonal mean winds, from year to year.

4. RELATION OF JET STREAMS TO SYNOPTIC SYSTEMS

Most of the discussion to follow will have to do with jet streams as­ sociated with the polar-front z~ne, for the simple reason that the more abund­ ant observations available in middle and higher latitudes have encouraged syn­ optic case-studies there rather than in subtropical and tropical latitudes. Naturally these studies have tended to emphasize the association between jet streams and frontal zones. Well marked polar fronts always have attendant jet 12 RELATION OF JET STREAMS TO SYNOPTIC SYSTEMS

streams, but the reverse is not always true. Thus the absence of surface fronts does not necessarily indicate the absence of a jet stream. This is particularly true of the subtropical jet stream, which appears to be a quasi-permanent feature of the circulation, affected in certain local­ ities by occasional intrusions of frontal jet streams from higher latitudes. An investigation by Phillips (1950) indicated that when polar-front jets migrate southward into subtropical latitudes, the associated low-level baro­ cline field gradually disappears, although baroclimity is maintained in the middle and upper troposphere. Experience with analysis in the Southern Hemisphere, where the subtropical jet stream is apparently the most important one, indicates that there are on the whole no attendant fronts. Thus any attempt to apply middle-latitude frontal models indiscriminately to the lower-latitude jet streams is likely to lead to confusion. Unless otherwise specified, the following remarks on synoptic systems are intended to refer to the systems of middle and higher latitudes. Extratropical Jet· Streams: Large-Scale Features. The well-known con­ cepts of long waves, with their attendant cyclone families, serve as a .useful guide to the general features of jet stream structure. There are usually 3 to 7 long waves around the hemisphere (Rossby and Collaborators, 1939; Cressman, 1948), with a corresponding number of large-scale waves in the jet stream. As noted by Staff Members, University of Chicago (1947), there is a fair­ ly close relationship between the meandering of the large-scale flow and that of the major barocline zone, or polar front zone. Since the latter is con­ nected with a jet stream, it follows that when the major waves have large amplitudes, with cold air in low latitudes in the vicinity of upper troughs and warm air extending into high latitudes in the vicinity of upper ridges, the jet stream itself is characterized by waves of large amplitude. Figure 4.1 (Bradbury and Palmen, 1953) shows a typical example of the isotherm pattern at 500 mb in winter, which brings out the meandering char­ acter of the polar-front zone, where the isotherms are most concentrated. Al­ though the jet stream does not exactly follow this isotherm ribbon, there is generally a close relationship in the broad features (the jet-stream axis tends to have a somewhat smaller amplitude than shown by waves in the isotherm band). The shapes of the waves in this figure vary from nearly sinusoidal over the eastern Pacific to highly irregular over Europe and North Africa, where a perturbation of very large north-south amplitude is observed. Examples of the development of irregular large-amplitude wave patterns are discussed in detail by Palmen and Nagler (1949), Berggren, Bolin, and Rossby (1949) and Rex (1950). The alternation between small- and large-ampli­ tude wave patterns with attendant variations in the strength of the mean hemi­ spheric westerly flow ("index cycle") is discussed by Namias (1947, 1950) and by Rossby and Willett (1948). No attempt will be made here to summarize the synoptic processes involved; a perusal of the references cited will suffice to bring out the great variations of the large-scale flow patterns and of the meandering jet streams. RELATION OF JET STREAMS TO SYNOPTIC SYSTEMS 13

Cressman (1950) found that in most cases there tend to be two principal jet streams around the hemisphere (on a given day these may appear to be joined over part of the hemisphere, and widely separated over other parts, with an average latitudinal separation of 10-20°). Cressman Lomputed daily average latitudes and strengths of the jet stream around most of the Northern Hemisphere at 300 mb for two periods of about 6 months each. He found that on the whole such hemispheric jet streams tended to form in higher latitudes, and to drift southward at a rate of one-half to two degrees latitude per day. In other instances, splitting of a pre-existing jet stream appears to occur, with a temporary poleward drift of one branch, followed by a movement south­ ward. The same behaviour was observed at SooW in a stuDY by Phillips (1950). The double (or sometimes triple) set of mean hemispheric jet streams ob­ served on a given map may in general consist of one jet which has been in existence for a long time and drifted far south, and another which has re­ cently formed in the north. During its latitudinal migration a marked varia­ tion of intensity is observed. Figure 4.2 is suggestive in this regard. This figure shows the mean latitude and mean strength of the jet stream at 300 mb for three warm and three cool months. For both periods a marked tendency is evident for the jet stream to have maximum intensity in middle latitudes. If the meridional drift of the jet stream is an accepted feature, it is clear that on the average the jets forming in higher latitudes strengthen consider­ ably in approaching middle latitudes, then weaken again on approaching the tro­ pics. It is not clear what implications, if any, Figure 4.2 has for the sub­ tropical jet, which is most pronounced at a higher level than represented in that figure. Smaller-Scale Features Relation to Cyclones and..,.Surface Frontal Svstems. Superimposed on the large-scale perturbations of the jet stream are smaller­ scale perturbations which tend to be associated in a general way with indi­ vidual wave cyclones. In line with the observation by Bjerknes and Solberg (1922), there may be several cyclones with one long wave (but sometimes only one; see Bjerknes 1951; Palmen 1951b), and ideally one would expect about the same number of smaller-scale jet stream perturbations associated with cor­ responding waves in the polar front zone. Although the relation beuNeen waves on the jet stream and the surface synoptic systems is not always this simple, the character of surface synoptic systems does serve as a useful guide as to what to expect in regard to the jet-stream pattern. Instructive examples of the relationship between jet streams and surface synoptic systems over the British Isles and environs have been given by Murray and Johnson (1952). Vederman (1954) has attempted to describe the general relationship between wave cyclones and configuration of the jet stream, com­ bining the material'of Murray and Johnson with experience from synoptic systems over North America. Figure 4.3, taken from Vederman, shows an idealized wave-cyclone family and the general relationship of the jet stream to surface cyclone and frontal systems at various stages of the development. As would be expected, when the wave cyclone is weak and its attendant frontal system has small amplitude, the jet stream (which more or less reflects the barocline field integrated through the troposphere) also has small wave amplitude. As a cyclone intensifies and 14 RELATION OF JET STREAMS TO SYNOPTIC SYSTEMS

increased amplitude is given to the mean thermal field, the jet-stream wave amplifies likewise. In the final stage of occlusion, according to Vederman, the jet stream tends to split into two branches ahead of the cyclone, as in­ dicated in the figure. Since it is characteristic of the ideal cyclone that at first the surface low is found at the wave peak On the surface front, while in the occluded and final dying stages the strong portion of the front moves successively farther and farther south with respect to the surface low center, a relative movement of the surface low across and finally to the left side of the jet axis is characteristic. As noted by Vederman and by Murray and Johnson, there are many compli­ cated variations in the jet-stream structure relative to a surface cyclone. However, as Vederman states, a general conception such as shown in Figure 4.3 is useful even if it does not apply in all cases, just as the wave cyclone model is useful although not universally applicable in the most rigid sense. Application of models is naturally of chief interest over areas such as oceanic regions, where direct aerologl.cal observations are sparse or absent. In general, as indicated in Figure 4.3, the jet stream lies closer to cold than to warm fronts at the surface. As pointed out by Palmen· (1948b), on the average the jet-stream axis tends to be found approximately above ~he intersection ·of the 500 mb surface with the warm-air boundary of a strong frontal layer; and, as noted by Murray and Johnson, this generally places the jet axis 200 to 400 mi (300-600 km) behind cold fronts and 400 to 800 mi (600­ 1200 km) in advance of warm fronts at the surface. The jet stream axis does not run parallel to a surface frontal system, but instead may lie quite close to the surface front near the peak of a warm sector, and farther away from the surface front with increasing distance upstream or downstream from the wave peak. It is frequently observed that the jet-stream axis may lie actually south of the surface wave peak, entirely within the warm sector over part of its length. Marked variations in wind speed generally occur along a jet axis; a striking example is shown in Figures 4.4 and 4.5. Here the thermal contrast in mid-troposphere (Figure 4.4) is highly concentrated in the southwestern United States, with a pronounced diffluence of the isotherms further east. Corresponding to the general features of the thermal wind field in Figure 4.4, a strong highly-concentrated jet (maximum speed 200 kt) is observed in Fig­ ure 4.5, south of Great Salt Lake. Further east, a rapid decrease in speed is observed, where the horizontal temperature gradient becomes weaker. Several localized jet maxima of the sort shown in Figure 4.5 may be found along a jet axis, over a length such as depicted in Figure 4.3. The wavy jet axis as a whole (if a regular pattern exists) will tend to move with the medium- and large-scale wave patterns. At the same time the individual speed maxima gen- . erally move downstream with a component along the jet axis (the main jet maxi­ mum in Figure 4.5 was moving eastward at the rate of about 30 kt). For ex­ amples of isotach analyses in different kinds of synoptic situations, see Newton and Carson (1953), Riehl et al (1954), Gazzola (1955) and Gibbs (1955). Connected with movements of this type, are changes in the wind structure of individual troughs and ridges aloft. During the development of a strong RELATION OF JET STREAMS TO SYNOPTIC SYSTEMS 15 trough in the upper troposphere (often in connection with surface cyclogenesis), the strongest winds are characteristically found on the west side; during the development the zone of strongest wind migrates through the equatorward side of the trough and in the final stage of development is generally found on the east side. Although in the schematic Figure 4.3 the jet stream has been drawn with a continuous axis, breaks in the jet axis are more the rule than the exception. In connection with the examples shown by Murray and Johnson (1952), these authors note that the jet stream associated with the cold front of a given cyclone may appear entirely disconnected from the jet stream over the warm­ front surface. Murray and Johnson find that the maximum wind at the jet-stream axis tends to be stronger by about 25 kt over a cold front than over a warm front. Although the number of cases involved is small, and the cases they studied were all in the vicinity of the British Isles and may be biased by the geo­ graphy of the region, this may quite generally be the case since cold fronts are usually steeper than warm fronts, with more pronounced average baroclinity through a deep layer. Relation of Jet Streams to Deep Tropospheric Frontal Layers. Although a general association is found between frontal systems and the jet stream, the relation is not always clear-cut. As noted by Palmen (195lb), a front which is strong at the earth's surface may be exceedingly vague in the upper tropo­ sphere, while a strong frontal layer in the upper troposphere may be only poorly reflected at the ground. In some cyclones, as noted originally by Nyberg (1945), the surface fronts may locally be only shallow phenomena during the early life of the cyclone. Thus, as pointed out by Riehl (1948b), the baroclinity associated with a distinct frontal layer may in an individual instance contribute only a minor part to the total thermal wind between the earth's surface and the level of the jet stream, most of the vertical shear being associated with weaker but still significant baroclinity through a deep layer of the troposphere within the individual air masses. Cross sections found in the literature show a great deal of variation, from jet streams as­ sociated with no distinct frontal layer to those associated with strong fron­ tal layers sloping upward through the entire depth of the troposphere. An example of the variations in frontal structure observed with a parti­ cular jet stream is shown in Figures4.6 and 4.7. These sections, 500 km apart on the west side of a weak surface cyclone, were observed in a situation very similar to that in Figures4.4 and 4.5, the corresponding locations being nor­ mal to the isotherms near the westernmost dashed line in Figure 4.4, and just west of the heavy dot in that figure (location of a surface cyclone). Figures 4.6 and 4.7 show in the one case a well-defined frontal layer extending through the whole troposphere, and in the other a shallow frontal layer confined to the lowest 300 mb. A section half-way in between (not shown), only 250 km from the upstream section, showed no upper-tropospheric frontal layer at all, and only a weak low-level front. The jet stream, on the other hand, is not much weaker in the downstream section than in the one upstream. Cle3rly one cannot make any general statement that the jet stream is or is not associated 16 RELATION OF JET STREfu~ TO SYNOPTIC SYSTEMS with fronts, since both statements may be true in different instances (see Reed and Sanders 1953) and even 'in different places along the same jet stream. It might be pointed out that the differences between Figures 4.6 and 4.7 do not merely involve a change in slope of the front; the upper part of the frontal layer in Figure 4.6 gradually became diffuse toward the east, with no marked change in slope, while the nearly horizontal stable layer in Figure 4.6 is a separate phenomenon entirely (the potential temperatures at frontal sur­ faces being about 20° different in the two cases). As noted in the preceding section, the location of jet axes with respect to surface fronts varies considerably from case to case. With the same cyclone and frontal system, this relationship is often observed to change markedly within a relatively short period of time. With particular regard to the cold front, a jet stream may be found in close proximity to the surface front during the early stages of a cyclonic development. Later, as the cold air sub­ sides and spreads out at the surface, with a pronounced change in frontal slope, the jet-stream axis may be found at a great distance from the surface cold front. The latter may be observed to move very far southward in a 24­ or 48-hour period, while the associated jet stream may at the same time under­ go little southward movement (see, e.g., Palmen and Newton 1951). It is clear that great caution must be used in attempting to relate jet-stream positions to those of surface fronts. In this regard, it is useful to construct frontal contour charts (Crocke~ Godson, and Penner, 1947) to show the structure of frontal surfaces a loft. Some very striking examples are given by Anderson, Boville, and McClellan (1955), showing the relationship of jet streams to frontal contour patterns. In the examples they show, distinct jetsare connected with the polar front and the arctic front; these jets combine and intensify markedly where the two frontal systems approach each other closely, with a combination of their solenoid fields. Over Japan and vicinity, a pronounced stable layer is frequently observed which has all the characteristics of a frontal layer but is confined entirely to the upper troposphere. Mohri (1953) has called this the "subtropical front", by virtue of its association with the subtropical jet stream. Figure 4.8 shows a remarkable example of the atmospheric structure at a time when this "front" has merged temporarily with the polar front, to produce'a pronounced stable layer over 5 km deep and 500 km wide. The "subtropical front" is observed on occasion at least as far east as the middle Pacific. This phenomenon may be confined to this particular geographical region, which is likewise the region having the strongest winds in the world. Note the deep layer of strong verti­ cal shear in Figure 4.8, culminated by winds in eXCess of 100 m/sec. As noted in Section 2, corresponding to the strong horizontal temperature gradient below jet-stream level there is a strong gradient of reverse sense above the jet. Berggren (1952, 1953) has proposed that the polar front can be analyzed as a single transition zone, as in Figure 4.9, dividing the tropical air, as an entity comprising both troposphere and stratosphere, from the polar air mass, also troposphere plus stratosphere. The polar stratosphere being warmer than the tropical stratosphere, this means that a front acting as a HORIZONTAL PROFILES THROUGH THE JET STREAM 17 warm front in the troposphere acts as a cold front in the stratosphere, as suggested by Bjerknes and Palm~n (1937). Near the maximum wind level, where the frontal layer reverses in slope, there is no horizontal temperature con­ trast (Figure 4.9). At this level, where the vertical shear is nil, the strongest horizontal shear is observed, according to Berggren. The exact nature of the zone of transition from polar to tropical air cannot be determined with confidence from routine aerological observations, because of the distance between stations, and the manner of analysis (compare Figures 2.1, 4.6 and 4.9) is to some extent a matter of individual preference. Eventually aircraft reconnaissance may throw some light on the exact structure of the temperature field. An analysis of the type indicated in Figure 4.9 is a useful concept regardless of whether the frontal boundaries are in all places clearly defined, since such an analysis brings out the principal fea­ tures of the zone of transition as a boundary between air masses both in troposphere and stratosphere, and the nature of this zone as one of marked cyclonic shear at all upper levels. As discussed in a later section, know­ ledge of the structure of the temperature field relative to the wind field, as depicted in Figure 4.9, has been found to be of considerable use in aerial navigation. All the examples shown above were taken from the middle-latitude polar front region. McIntyre and Lee (1953) show a cross section through the arctic front (with warm-air temperatures of -33C at 500 mb compared with -15C in Fig­ ure 4.9) which is in all essentials similar to the characteristic structure in middle latitudes (including tropopause configuration). They present data sug­ gesting that such frontal jet-stream systems may move southward with a gradual transformation to warmer air masses (cf. Cressman, 1950, Phillips 1950).

5. HORIZONTAL PROFILES THROUGH THE JET STREAM WIND SHEAR AND VORTICITY DISTRIBUTION

Knowledge of the typical values of horizontal wind shear to be expected in the vicinity of the jet stream is not only of theoretical interest, but also of very considerable practical importance. On the whole, aerological wind observations tend to be more sparse and less accurate where the upper winds are strong. If some general rules could be derived for construction of the wind profile, it would be possible to analyze the wind-speed field by use of a few wind observations quite distant from the axis of maximum wind; such general knowledge as is available has been used on a routine basis by some analysts for several years. Profiles from Aerological Analyses. The general character of the hori­ zontal distribution of wind through the jet stream at different levels is re­ presented by Figure 5.1. The wind profile is seen to be characterized by a rather sharply-peaked maximum, with strong shear on both sides of the jet­ stream core, the gradient of speed decreasing in general with increasing dis­ tance from the axis of maximum wind. This figure is derived from a mean cross 18 HORIZONTAL PROFILES THROUGH THE JET STREAM

section constructed from 12 winter cases, the temperature field having been averaged with respect to a system of coordinates fixed to the polar-front layer. Although this method preserves the major features, the extreme values of horizontal shear are to some extent damped. In Figure 5.1 the maximum "peakedness" of the wind profile is seen at 300 mb, near the level of maximum wind. The strongest cyclonic shear is found there and in the upper part of the frontal layer. As noted by Palmen (1948b), the axis of strongest wind tends to be found nearly above the warm boundary of the frontal layer at 500 mb. The zone of strongest anticyclonic shear, 2-300 km from the jet axis, frequently lies nearly over the front at 700 mb, and by hydrostatic reflection the cyclonic shear within the front tends to be weakest near that level. Thus in Figure 5.1 the shear at 500 mb through the frontal layer is more than double that at 700 mb. Other things being equal, the intensity of the cyclonic shear bordering the jet stream appears to be greater in cases where there is a pronounced front than when there is not. As seen from Figures 4.6 and 4.9, the pro­ nounced vertical shear found within the sloping frontal layer is also associ­ ated with marked horizontal shear. Figure 4.6 may be compared with Figure 4.7, where the front is absent in the higher troposphere, and both the verti­ cal and horizontal shear are weaker. Magnitudes of Shear and Vorticity. At the level of maximum wind, many aerological analyses supported by gradient wind computations and by observed winds have shown that the absolute vorticity tends to reach a limiting value near zero on the anticyclonic side of the jet stream at varying distances 100 to 400 km from the jet axis. The absolute vorticity may be expressed as f + ~~ + ~ f being the

Coriolis parameter 2 w sin 0; V, the wind speed; {)V , the wind shear (posi- ()n tive for cyclonic shear); and R, the radius of streamline curvature (positive cyclonic). Thus in straight flow, the maximum anticyclonic shear 100-300 km from jet axis (see Figure 2.1) has about the same value as the Coriolis para­ meter (order 10 m/sec or 20 kt in 100 km near latitude 450). Such analyses as are available indicate that the anticyclonic shear is stronger for cyclonically curved, and weaker for anticyclonically curved streamlines, than the limiting value for straight flow, suggesting that the shear and curvature combined tend to reach the limiting value -f. With very strong winds in intense troughs, where the curvature term in the above expres­ sion sometimes approaChes the value of f, the anticyclonic shear may thus be up to about 2xlO-4 sec-lor 20 m/sec in 100 km. The observation that the absolute vorticity does not go negative is in good agreement with expectations from the criterion for "dynamic instability", first developed by Solberg (1939) and later amplified by Kleinschmidt (1941), Van Mieghem (1951) and others. This criterion predicted that lateral instabi­ Iity should develop if the vorticity of the gradient wind field should go be­ low zero; in that case the condition of instability should be destroyed in the HORIZONTAL PROFILES THROUGH THE JET STREAM 19

same way that strong superadiabatic lapse rates tend to be eliminated by ver­ tical exchange. Strictly speaking, the vorticity concerned should be that in an isentropic surface (Bjerknes, 1951), so that above or below the level of strongest wind the limiting value of anticyclonic shear in a level surface is somewhat weaker than indicated by the above criterion. While the magnitude of anticyclonic shear seems to be restricted by the condition of zero absolute vorticity, there is no known theoretical restric­ tion on the magnitude of the shear which may be attained on the cyclonic flank of the jet stream. On the average, the shear is considerably stronger on the cyclonic than on the anticyclonic flank; with a pronounced jet the velocity profile is particularly asymmetrical. Analyses from aerological observations suggest that the maximum absolute vorticity on the cyclonic flank (when gradi­ ents of velocity are measured on "synoptic scale" of 100-200 km) is 2 to 6 times the Coriolis parameter in practically all cases; this is probably ex­ ceeded in some. Berggren (1952) gives for Figure 4.9, within the vertical part of the front at tropopause level, shear of 45 to 60 m/sec (up to 115 kt) per 100 km horizontal distance, based on observed winds. Vuorela (1953) finds comparable values. In Figure 5.1 the greatest horizontal shear near jet level is about 15 m/sec per 100 kmj this would be an underestimate for the indivi­ dual cases involved. Murray and Johnson (1952) and Johnson (1953d), from mean profiles con­ structed from a large number of cross sections, find that over distances of roughly 400 km from the jet axis the cyclonic shear averages about 1.5 times the value of the anticyclonic shear. Over smaller distances, the shear would of course be larger. According to Hsieh (1950b), the value of the horizontal shear tends to be somewhat smaller in ridges than in troughs. The most extreme development of atmospheric troughs is the formation of shear lines, where oppositely-directed jet streams with speeds of the order 100 kt are found close together. With a well-developed shear line an average shear of around 20 m/sec per 100 km (Murray and Johnson 1952; Newton, Phillips, Carson and Bradbury 1951) may be observed over the characteristic distance of 500-600 km separating the jets. Murray and Johnson note that on the average for the cases they analyzed, the distance from the jet axis out to the place where the wind speed drops to one-half its maximum value is about 300 km on the cyclonic side, and 500 km on the anticyclonic side of the jet. These distances agree very closely with the corresponding "half widths" at 300 mb in Figure 5.l. MUltiple Jets. As noted earlier, there tends to be more than one major jet stream observable at a given meridian at a particular time. Figure 5.2 shows a typical example of two principal jet streams, each having localized maxima of wind speed along its axis. The individual jet stream systems may include the subtropical jet, and one or more jets connected with the polar, arctic, or other frontal systems. Connected with an individual frontal system there is often observed, instead of a single jet stream as suggested by the idealized Figure 4.3, two more-or-less parallel jet streams separated by 500­ BOO km distance (Gustafson 1949). Jet streams associated with separate wave 20 HORIZONTAL PROFILES THROUGH THE JET STREAM

or frontal systems in different latitude belts may also lie in close proximity over parts of the weather map. For a discussion of the streakiness of atmo­ spheric and oceanic currents, see Rossby (1953). Figure 5.3 shows a cross section through three jets which happened to lie close together in one locality (diverging sharply a short distance downstream from the section). In this case, the wind data up-and downstream from the sec­ tion showed the discrete natures of the individual jet streams, each charac­ terized by cyclonic and anticyclonic shears of the magnitudes typical for single jet streams. It is not always possible to distinguish between the in­ dividual jets, however, and it is COmmon practice to "merge" two wind maxima into one, where they come into close lateral proximity on an isotach chart. Whether this actually occurs is often not determinable from the observations. Whether or not two separate jets are present in the vicinity, such a "con­ fluence" (Namias and Clapp, 1949) is associated with lateral concentration of the thermal field, and the upper-level winds tend to be strongest downstream from a zone of confluence and upstream from a diffluent zone. As shown by Anderson et ~ (1955), such a reinforcement of the thermal field, and ~rength­ ening of the upper winds, frequently occurs where the arctic- and polar-front zones lie close together. As noted by Riehl and Teweles (1953), in cases with very strong winds in one maximum (e.g. 150 kt) the tendency is for only a single jet to dominate a region of the size, say, of the United States. On occasions with weaker winds, say 60-75 kt maximum, several collateral jet axes or "fingers" may be observed in a comparable region. As illustrated by Figure 4.5, downstream from a large and strong jet maximum, where marked deceleration occurs, the wind field may degenerate into such minor fingers several hundred km apart. Jet-Stream Profiles from· Aircraft Reconnaissance. The wind profiles in Figure 5.1 were computed using the geostrophic wind relationship. When ana­ lyzing the wind field by use of the regular network of radiosonde and upper wind stations, one is faced with the possibility that some details of the temperature and height fields may either be smoothed out in the analysis Or not shown by the data in the first place. The question then arises to what extent details in the wind and temperature fields may exist, which are not shown by the aerological network. To attempt to answer this question and other related ones, several extensive aircraft reconnaissance programs have been and are being carried out. The discussion here will be concerned only with the wind field, which has been explored chiefly in reconnaissance programs of the U.S. Air Force and U.S. Navy. Other extensive programs, such as the Meteorological Research Flight from Farnborough, England (Murray, 1956) and those discussed later in the section on turbulence, have not had investigation of the wind field as their primary aim. Murray states that the flights generally confirmed the pic­ ture presented by cross sections from routine upper air data, but do not add much to existing ideas on the thermal structure in the vicinity of the jet stream. Measurements of winds by aircraft depend essentially, in all methods used, upon computing the wind drift from the difference between vector ground track HORIZONTAL PROFILES THROUGH THE JET STREAM 21 of the aircraft, and its movement relative to the air as indicated by true air speed and heading. Very great care must be exercised in interpreting the re­ sults of such wind measurements, to take cognizance of the degree of possible error involved. It is generally impossible, from the published data, to form any impression of the errors due to faulty airspeed measurement or compass calibration, which are not necessarily negligible (see discussion by Rutherford, 1956). Errors in ground tracking, however, are generally assumed to contribute the major part to errors in wind computations. In jet streams reconnaissance, fast aircraft are used in order to minimize the effect of time variations of the wind and temperature fields, in determin­ ing the space variations. A primary objective being to study the space dis­ tribution in more detail than is possible by use of the aerological network, it has been held essential to make measurements over as short segments of a flight as feasible, such segments usually corresponding to t to 2 minutes fly­ ing time (it has generally been found necessary to smooth over greater inter­ vals than planned, in evaluating "the data). Several methods have been used in determining ground speed and direction of flight : vertical photography of the underlying surface; triangulation by bearings on (or from) ground radio stations; and use of a radar device aboard the aircraft which utilizes the Doppler effect to compute movement with res­ pect to identifiable ground targets. Use of the first method is naturally confined to situations wherein there is little cloud cover beneath the air­ craft, and therefore in general to restricted types of synoptic situations. While it is not possible to go into detail on the various methods of na­ vigation, it is at least appropriate to comment on the fact that small errors in position fixes can result in appreciable errors in wind determination. For example, a cumulative error in navigational fix 'of only 0.5 nautical mile between two points at one minute intervals of a flight path would result in a vector error in wind determination amounting to 30 kt. In at least one exten­ sive flight program, the probable errors in fix were greater than this, ob­ viating the possibility of investigating the small--scale structure of the wind field. The broad results of aircraft reconnaissance of the jet stream have veri­ fied the general character of the wind profiles, such as shown in Figure 5.1, that have been computed from aerological data. The principal questions appear to be in regard to details, e.g. whether the wind profile is sharply peaked or rounded, and whether the profile has a regular smooth shape, or is charac­ terized by a "micro-structure" reflecting significant fluctuations of the wind about the smoothed profile. . The earliest published aircraft measurements of wind in flights across the jet stream are those by Hurst (1952, 1953), the fixes being determined photo­ graphically. A wind profile from one flight over Great Britain is shown in Figure 5.4. Hurst (1953) estimates that the probable error due to effect of variations in altitude and heading of the aircraft upon the photographic fix was 3.5 kt, and that the derived winds "are not inconsistent with a smooth velocity profile". 22 HORIZONTAL PROFILES THROUGH THE JET STREAM

Figure 5.5 shows a composite 300 mb profile obtained by Riehl (1955) by combining Hurst's results with those from several reconnaissance flights by U.S. Navy aircraft. In the Navy flights, fixes were obtained by triangulation from radio stations ("Omnirange"). Measurements made at frequent intervals indicated very large fluctuations in the derived winds, but it was found that these could for the most part be ascribed to errors in fix, which were of the order 2 nautical miles, and often larger. Such fluctuations were consequently rejected by Riehl et £1 (1955), and the profiles in Figure 5.5 represent a considerable smoothing of the original data. The peak wind of 244 knots in Figure 5.5 was the strongest measured on any of the Navy flights. An exhaustive examination of this case (Riehl et al 1955; see also more extensive discussion by Riehl and Maynard, 1954) shows that it was impossible to fit the results of this aircraft flight into an ana­ lysis for the corresponding time utilizing the regular aerological winds. Thus it is ,necessary either to conclude that the aircraft measurements indicated winds very much too strong over the flight path as a whole, or that the sur­ rounding aerological wind observations over a large area indicated systematic­ ally very much (20-100 kt) too weak speeds. Which of these alternatives is preferable is not indicated by the authors; although they state that the re­ connaissance results were consistent with gradient winds computed from the pressure field. Analysis of further results from the same flight program (U.S. Navy, 1955) discloses considerable variety in the shape of the wind profile across the jet stream. In contrast to Figure 5.5, some flights indicated blunt, rather than sharply peaked, wind maxima. The investigators attribute the difference in character largely to the fact that some flights were made across the "tail" or upstream portion of jet maxima, while others were made across the region of the strongest winds, or in the "nose" or downstream portion. Two of the five "blunt" profiles were in the tail portion, the others being across the central portion. In general, the flights across the noses of jet maxima showed a con­ siderably less well-defined character than that in Figure 5.5, with weaker shear on the cyclonic side. A question which cannot be answered by analyses of regular aerological observations is that of small-scale"streakiness" in the wind field. Attempts have been made to analyze the micro-structure of the wind field on the basis of reconnaissance measurements by U.S. Air Force planes equipped with Doppler radar systems. With such equipment, essentially instantaneous wind computa­ tions are made by the automatic-computing navigation system of the aircraft. Most of the published analyses show observations at about 30-km intervals. Some results have been presented by Endlich et Ql (1954), Landers (1955), Brundidge (1956), Cunningham (1956a) and Saucier et al (1956). An example is reproduced in Figure 5.6, constructed from the results of flights at 280 and 380 mb. Isotachs from conventional aerological data (dashed lines) agree rather well with the broad scale results, considering the differ­ ence between observation times. With regard to the fine structure, Landers (1955) states, "The striking features on this Cross section are the three cen­ ters of maximum speed within the large-scale jet stream. All three of these HORIZONTAL PROFILES THROUGH THE JET STREAM 23 maxima were evident in the data at both the 400 and 300 mb levels, therefore their existence cannot be denied '" The fine structure is missed completely when we are restricted to the normally available winds". When judging the significance of Figure 5.6, in which the variations from a smooth wind-speed pattern are of the order 5 to 10 kt, it is appropri­ ate to note that Endlich et 21 (1954) indicate an accuracy for the wind com­ putations of=e 5 kt and~ 10 degrees. An examination of all published ana­ lyses from this project indicates that with the exception of one example show­ ing two closely adjacent jets of almost "synoptic" scale (Figure 10 in Endlich et 21), the irregularities of the wind profiles are either of small magnitude and scale as in Figure 5.6, or else of a completely chaotic nature (comparing flights at different levels) which throws doubt on the accuracy of the obser­ vations. When the small-scale irregularities are smoothed by the amount of the ex­ pected degree of accuracy, the Air Force reconnaissance flights mostly yield rounded profiles of maximum wind, in contradistinction to the peaked profile shown in Figure 5.5. It does not appear that the evidence published either conclusively sup­ ports or denies the existence of small-scale (dimensions 25-50 km) variations of wind speed, of the order 10 kt, superimposed on a regular profile such as that in Figure 5.1 Or Figure 5.5. Since the latest observational material does not show larger variations, and the data of Hurst (1952) indicates even smaller ones, it appears justifiable to conclude that the wind-speed anomalies are no greater than 10 kt, and probably smaller. Supposing that the velocity fluctuations do exist, the question might be asked whether they are extensive over significant distances up- and downstream, and whether they persist in time as individual entities. For a discussion of the reality of small-scale streakiness, the reader is referred to Saucier and Riehl (1956) and the back­ ground references given. Aside from the details of the wind profile, both reconnaissance programs (Endlich et ~ 1954; Riehl et al 1955) have yielded data to show that the in­ tegrated winds over 300-500 km segments of the flight paths are better repre­ sented by the gradient than by the geostrophic wind. Wind Shear and Vorticity Values Revealed by Aircraft Flights. On the basis of the aircraft measurements summarized in Figure 5.5, Riehl and Col­ laborators concluded that the maximum absolute vorticity is proportional to the maximum wind in the jet axis; for the cases shown, the maximum absolute vorticity varies from 3 x 10-4 sec-l (Hurst 1953) to 8 x 10-4 sec-I. As noted earlier, the wind profile for the February 27 flight corresponding to the last value was at considerable variance with the surrounding data from the regular aerological network. A feature of the profiles in Figure 5.5 is that the cyclonic vorticity decreases with distance from the jet axis. In some subsequent flights in the same reconnaissance program (U.S. Navy 1955), the greatest vorticity values were indicated at least 200 km to the left of the wind maximum. 24 VARIATION OF WIND IN THE VERTICAL

On the anticyclonic flanks of jet streams, the aircraft measurements have substantiated the existence of near-zero absolute vorticity, over distances of 300-500 km or more from the jet axis. Taking the results of the reconnaissance programs together with the re­ gular aerological investigations, it is obviously too early to attempt to gen·· eralize on the empirical laws governing the shapes of wind profiles, and the exact character of the vorticity field. Nevertheless, enough is known about the characteristic form of the wind profile to enable a skilled analyst to derive a useful approximation to the wind speed pattern, from aerological data at points relatively far apart.

6. VARIATION OF WIND IN THE VERTICAL

Relation between Jet Axis and Tropopause Height. Bassus (1906) was one of the earliest investigators to note the marked decre~se of wind speed with height above the tropopause. Dobson (1920) observed that the level of maximum wind was closely allied to the tropopause, and deduced the characteristic re­ versal of direction of the horizontal temperature gradient through the tropo­ pause. The general relation between jet streams and tropopauses has been treated in a host of papers, some of which have been mentioned in earlier sec­ tions. Investigations of aerological data over Europe (Austin and Bannon 1952; Coudron 1952; Faust 1953; Bannon and Jackson 1953), the southwestern United States (Gutenberg 1949), and at Amsterdam Island in the South Indian Ocean (Viaut 1954) indicate rather uniformly that on the average the level of maxi­ mum wind is found about 1 km below the tropopause level. Correlation coefficients and frequency diagrams relating tropopause height or pressure with the maximum wind level reveal only a feeble correlation for collections of individual observations (Endlich et al 1955). Coudron (1952) found from observations over France that with maximum wind speeds less than 50 m/sec there is a very strong tendency for the peak wind to be located with­ in 1 km below tropopause level, while for "jet-stream winds" greater than 50 m/sec the wind maximum ranged from 1 km above to 4 km or more below the tropo­ pause. This is not surprising, considering that the jet axis lies in the re­ gion of transition between high tropical and low polar tropopauses ~igure2.1). Character of Vertical Wind Profile. The precise nature of the variation of wind with height is, of course, strongly dependent upon the structure of the temperature field. Thus, while the isotachs in Figure 4.7 indicate a re­ latively uniform increase of wind with height up to jet level, those in Fig­ ure 4.6 and particularly Figure 4.9 show a strong concentration of the verti­ cal shear within the frontal layer (observed vertical shear 33 m/s per km be­ tween 400 and 500 mb). Figure 5.1, where the shear is indicated by the verti­ cal spacing between the wind profiles for successive isobaric surfaces, sug­ gests that (e.g. at latitude 45°) about one-third of the total increase of wind between the ground and jet level takes place through the frontal layer. VARIATION OF WIND IN THE VERTICAL 25

Several investigators have computed average vertical profiles of the wind speed in the vicinity of the jet stream, notably U.S. Navy Project AROWA (1955), Endlich et ~ (1955) and Reiter (1957a). While there is some varia­ tion in the results, the crude features of the average profiles appear quan­ titatively to be in fair agreement. Figure 6.1 shows one such profile, taken from the Navy report. This profile is one of nine prepared for various loca­ tions with respect to the wind maximum; although only 9 soundings are repre­ sented by this particular figure, it was selected because the decay of wind speed above and below the level of maximum wind happened to be most repre­ sentative of the average results from a large number of cases used in the three investigations mentioned above. The results of the three investigations, taken as a whole, suggest that on the average the wind speed drops to about half the maximum value, at le­ vels about 5 km above and below the level of strongest wind. The decay with height is slightly more rapid above, than below, the level of maximum wind (compare Figure 3.4). In Figure 6.1, the dashed lines are the envelo?es for only 9 cases; it is immediately seen that one must be very careful in using mean profiles for constructing the wind field in individual cases (some of the variability is, of course, associated with random observation errors). Separating a large group of observations according to maximum wind speed reached (peak speed in all cases 80 kt or more), and constructing mean pro­ files for each speed class, Endlich et al (1955) found that there was no significant variation in the shape of the wind profile in the various classes according to wind speed. Project AROWA (1955) found that there is a signifi­ cantly larger average increase of wind with height in the upper troposphere on the cyclonic than on the anticyclonic side of the jet axis (wind at 20,000 ft below level of maximum wind averaged 36 per cent of speed at level of maximum wind on cyclonic side; 45 per cent on anticyclonic side). This finding agrees with the concensus of analyses of cross sections, most of which have indicated strongest vertical shear on the cyclonic flank of the jet stream. The studies above indicate that the average wind profile may for practi­ cal purposes be regarded as linear, within 200 or 250 mb below the level of maximum wind, with a vertical shear proportional to the speed at the level of maximum wind. Beneath a wind maximum of 150 kt (75 m/sec), the shear would thus on the average be about 7 or 8 m/sec per km. Immediately above the level of the tropopause, the vertical shear is somewhat stronger, with a gradually decreasing shear at higher levels. If a frontal layer is present, the vertical shear through it (winter) is commonly about 15 to 20 m/sec per km, or about twice the value observed above the front in the region of strongest wind (see Figure 5.1). The shape of the wind profile may vary strongly in different situations. In contrast to the mean profile characterized by Figure 6.1, stands that in Figure 6.2. This type of profile, showing hardly any vertical shear through most of the troposphere, is common in the tropics and is observed occasionally in middle latitudes in summer. In the latter case, a profile of this type may 26 VARIATION OF WIND IN THE VERTICAL

characterize only the cyclonic flank of the jet stream, while the anticyclonic flank may exhibit a more uniform distribution of vertical shear. Malkus and Ronne (1954) show a striking example of the vertical wind distribution in the subtropical jet, having the character of Figure 6.2; vertical shear up to 30 m/sec per km was observed in the case they show. Endlich et al (1955) found that the level of maximum wind in their sample (cases from entire United States, November 1952 through March 1953) had a marked frequency maximum near 215 mb, with a total variation from 345 mb to 120 mb (27,000-50,000 ft). Johnson (1953b) presents a case where the strong­ est wind was observed at the unusually low level of 18,000 ft near a deep cy­ clone. Low Tropospheric and High Str~tospheric Wind Maxima. Means (1954) dis­ CUsses a "low-level jet" having the same general characteristics as the typi­ cal jet streams discussed earlier. This low-level wind maximum occurs com­ monly at around 850 mb in North America (entirely within an air mass) and over the Great Plains area sometimes reaches speeds of 90 kt or even more. Above it, the wind speed characteristically decreases up to the 700 mb level, then increases again with height above that level· (in a different wind system). H. Arakawa (1956) has noted that on occasion in Japan two distinct wind maxima are observed in the vertical profile; the uppermost near tropopause level and the lower one in mid-troposphere. The lower-level maximum is associ­ ated with some sort of frontal layer which is surmounted by a layer in which the horizontal temperature gradient reverses. In an example, there were maxi­ ma of 60 m/sec at 7 km, and 75 m/sec at 13 km. A somewhat similar distribution is shown in the North Atlantic by Defant and Taba (1957), who suggest that ver­ tical profiles of this sort are found where the polar-front and subtropical jets (with their accompanying tropopause structures and thermal fields) lie in close horizontal proximity. In winter, as noted earlier in connection with Figure 3.4, a high-level wind maximum is found in the stratosphere in the subpolar regions. Figure 6.3 shows a very striking example of this "polar night" wind maximum, with speed 160 kt and all the characteristics of a jet stream. Note that the winds at tropopause level are very weak, all the vertical shear being found above it where a deep isothermal layer extends up to 25 mb, the level of maximum wind. The temperature gradient between stations 072 and 082 is about 20C in 10° latitude distance. Details in the Vertical Wind Profile; Accuracy of Wind Soundings. The same questions arise in the case of the vertical as in the case of the horizontal profiles of wind speed, namely, how sharp is the wind profile at the level of maximum wind, and the question of reality of irregular large fluctuations of the wind speed. The characters of the horizontal and vertical profiles may in fact be related, in the senSe that if irregularities of large magnitude exist in one, they very likely exist in the other. Wi thout commenting on any particular type of equipment, it is appropriate to draw attention to the stringent requirements placed upon wind finding equip­ ment in the measurement of strong winds at high altitudes. With strong winds, VARIATION OF WIND IN THE VERTICAL 27

it is quite common for a meteorological balloon to be observed at angles less than 10° above the horizon, when the balloon is at high altitudes. At this elevation angle, if the balloon is at 12 km height and its elevation is meas­ ured incorrectly by 0.1°, a trigonometric error of position amounting to 720m will result. Two successive noncompensating errors of this size, at one­ minute intervals, would lead to an error in wind computation of 24 m/sec or 47 kt. In principle, modern automatic direction-finding equipment is capable of measuring angles with an estimated accuracy of~ 0.05° or less (Ference, 1951). Unfortunately, derangement of calibration takes place in field use, and tests at field stations often show much greater fluctuations of an obviously spur­ ious nature, as vividly illustrated by the wind profile in Figure 6.4 (Reiter, 1957a). While this is an extreme example, irregular fluctuations of 20 to 50 kt in 1-2000 ft are Common with radio direction-finding equipment under strong wind conditions (see, e.g., specimens shown by Clem, 1954). In view of the variability of types of equipment and of operating conditions, no categorical statement of the size of errors can be made. Thus one can never be certain what part of the irregularities such as shown in Figure 6.4 are real, but there is a strong presumption (supported by unpublished records and hearsay reports of station equipment tests) that the fluctuations are mainly spurious and should be disregarded. The seriousness of the problem of representative­ ness of wind soundings has been recognized by the official weather services, and improvements (considering the character of the equipment, largely having to do with faster-rising balloons and larger smoothing intervals) Can fortun­ ately be expected. Meanwhile, it is essential to realize the limitations of the available wind reports. The consequence of not taking a realistic view of these limitations is brought out by comparison of the transmitted wind report (Figure 6.4) with the original speed profile. The message sent for upper le­ vels, using the present coding technique, depends largely upon random circum­ stances in just where a standard level lies on the plotted sounding curve. As Reiter points out, the selection of standard levels for transmission at, say 500 m higher, would have resulted in an entirely different wind profile with apparent levels of maximum wind elsewhere than indicated by the profile for the coded report in the figure. The manner of selection of winds at standard levels for broadcasting seriously affects the quality of individual wind re­ ports used in constructing constant-level or isobaric analyses. The above remarks are intended to apply to visual or radio direction-find­ ing methods, which are used at the bulk of the wind-finding stations in most regions. Radar and radarsonde observations, in which the slant range is meas­ ured and which are not so critically dependent upon the accuracy of measure­ ment of angle (Jones, 1949), are inherently very much more accurate. Winds measured by the British (radar) system, for example, do not show the great fluctuations as in Figure 6.4. In light of what has been said above, it is evident that nothing can be said with assurance about the sharpness of the wind profile at the peak wind speed, the determination of which would depend upon very accurate measurement of speeds at close height intervals which are in principle impossible with 28 CLEAR AIR TURBULENCE AND THE JET STREAM

ordinary wind-finding equipment. Thus for example the contention by Endlich et.i!l (1955) that there isa sharp peak at jet level, with an abrupt change from a rather uniform increase of wind with height below to a pronounced de­ crease with height above maximum wind level, rather than a more moderately rounded wind profile as suggested by cross-section analyses, can neither be confirmed nor disproved by the wind observations. In this regard, it should be pointed out that if the wind field conforms at all well to the geostrophic or gradient-wind relationship,a sharp peak is to be expected only under spe­ cial circumstances. A discontinuity in the vertical shear, as shown.by Palmen (1948b) would only be expected on a surface through which there is an abrupt discontinuity of the horizontal temperature gradient. A sharp peak of the wind profile is thus to be expected only where the strongest wind coincides with a sloping tropopause. As noted earlier this is not usually the case, the jet being in most cases found some distance below the tropopause. Maximum Observed Wind Speeds. In popular press and radio accounts, the jet stream is often described as having characteristic speeds of 300 kt or more. Several widely publicized upper wind observations have indicated speeds greater than this value. The U.S. Air Weather Service (1955) reports that all such cases which have been checked have proven to be erroneous. The excessive speeds may be due to oscillations in angular measurements by direction-finding equipment, such as involved in Figure 6.4, or to a vari­ ety of other causes. An important contributing cause, only recently recog­ nized, is failure to take the sphericity of the earth into account when com­ puting the horizontal distance to a balloon. This factor tends to make "flat earth" trigonometrically-computed distances and speeds too great. Under Com­ mon conditions (see Gustafson 1954), if sphericity is not taken into account an overestimate of 30 to 40 kt can result, if the wind is 200 kt at jet-stream level; the error is greater for stronger winds. On the other hand, bona fide wind speed measurements in excess of 200 kt have been made on many occasions (for a synoptic example, see Foster and Robinson 1953). The Air Weather Service report (1955) lists four legitimate observations of speeds greater than 250 kt in the Northern Hemisphere. Two of these were made at Tateno, Japan, using a system by which a balloon is re­ leased at Honjo (88 km west) and observed in relay by Honjo and Tateno sta­ tions. Since the ~ maximum speed in the jet over southern Japan in winter is around 180 kt, it is likely thBt speeds up to 300 kt may occur on occasion. In the run-of-the-mill winter jet streams of the Northern Hemisphere, local maximum velocities reached appear usually to be between about 140 and 200 kt (for a regional appraisal, see Cunningham 1956b); while in summer the charac­ teristic maxima are 1/2 to 2/3 these speeds.

7. CLEAR AIR TURBULENCE AND THE JET STREAM

Clear air turbulence can be experienced at all altitudes from the ground up to the ceiling level of conventional aircraft. In lower levels it is ob­ vious that turbulence may OCCUr during certain meteorological conditions and CLEAR AIR TURBULENCE AND THE JET STREAM 29 it is mostly foreseen by the pilot. Thus, he has time to reduce the speed of the aircraft and to be on the alert in this respect. At higher levels, how­ ever, clear air turbulence most often occurs without any warning whatsoever to the pilot. Thus, the aircraft enters the turbulent region with a normal cruising speed, which means that the effect of the turbulence on the aircraft at times may be severe. During the last ten years a number of papers dealing with the problem of clear air turbulence have been published. Most of them only discuss reports from an altitude greater than, say, 4000 m. For the discussion in this paper, howev~r, this restriction has no negative effect. Before going into more details a discussion of the difficulties one en­ counters when studying the problems of clear air turbulence must be mentioned. Most of the published reports of clear air turbulence come from western Europe and the North American continent, with a few scattered reports from other locations. The reports represent, however, a very heterogeneous sample. The type of aircraft and the height of the turbulence regions vary consider­ ably and sometimes the reports fail to give these details. The number of re­ ports is as a whole rather limited, and furthermore they most often represent positive reports. The fact that a report is not available for a certain re­ gion and for a certain time can mean either that (a) no turbulence was ob­ served, (b) turbulence was observed but not reported, or (c) no aircraft was at the specified location at the specified time. A comparatively small percentage of the turbulence reports give the ef­ fect of the turbulence on the aircraft in terms of accelerometer readings. Most often only subjective measurements are given. An example of the subjec-­ tive definitions are given by the following list, which can be found on an ICAO form: slight (perceptible), moderate (difficulty walking), and severe (objects thrown about cabin). Finally it must be emphasized that the study of the meteorological condi­ tions prevailing in areas with turbulence is hampered by two effects. First the upper air network is sparse even in areas where it is densest; secondly, the turbulence reports are most often not synchronous with the meteorological reports. The above-mentioned difficulties have been allowed for in different ways. One of the first attempts to tackle the problem of clear air turbulence was made by the British European Airways. In this case a Mosquito aeroplane was sent out on search flights on the different BEA routes in Europe (Hislop, 1951), using a systematic flight technique in order to insure a maximum pos­ sibility of encountering turbulence. In the test period discussed by Lake (1956), the attempt was made to get a maximum number of reports at the hours of the upper air soundings (0300 and 1500 GMT). Many others have picked out only those reports that are within a reasonable distance in space as well as in time from an upper air sounding. When studying the meteorological conditions in connection with turbulence reports different authors have put the emphasis on different meteorological variables. The importance of low values of Richardson's number (proportional 30 CLEAR AIR TURBULENCE AND THE JET STREAM

to thermal stability and inverse of vertical shear) has been stressed by some (Bannon, 1951b, 1951d; Jones, 1954; Hislop, 1951), while others have disre­ garded the vertical stability and only considered the vertical wind shear (Mook, 1952). Lake (1956) studied the vertical gradient of the horizontal kinetic energy and the product of the horizontal wind speed and the vertical gradient of the wind shear. The importance of horizontal wind shear has been mentioned by many authors : (Bannon, 1951b, 1951d; Berggren, 1952; Harrison, 1950, 1951; Mook, 1952; Arakawa, 1953). In some papers a discussion is given about the connection between turbulence and the tropopause (Bannon, 1951d; Hislop, 1951), and in others between turbulence and fronts (Aanensen, 1948; Berggren, 1952; Frost, 1953; Pothecary, 1953). It would lead too far to discuss in this paper the many aspects of the very complex question of clear air turbulence. The reader is referred to the above-mentioned papers by Hislop (1951), Mook (1952), Lake (1956) as well as to a detailed study pUblishedby Chambers (1955). The latter author gives many examples of cases with turbulence together with corresponding upper air charts. He states that clear air turbulence has not been a problem on BOAC flights over the London-Far East and the London-South Africa routes. By definition a jet stream is connected with large values of the hori­ zontal and vertical wind shear. From the discussion above it is therefore clear that an aircraft flying in a jet stream area in many cases may encounter clear. air turbulence. In this connection two questions immediately arise. First, what is the probability that clear air turbulence will be encountered by an aircraft flying in a jet stream, and second, in which part of the jet stream as seen in a Cross section will the turbulence most likely occur? The first question is not dealt with so much in the literature. Some fig­ ures may, however, be quoted. According to Hyde (1954), clear air turbulence was observed in· 40 per cent of the cases when a jet stream existed in the area covered by the flight. Jones (1954) discusses special flights made through jet streams over the British Isles. Out of 30 such flights 28 were successful; that is, the aircraft encountered clear air turbulence. Of the 28 cases, one­ third contained reports of slight turbulence, one-third gave moderate turbu­ lence and one-third severe turbulence. In Chambers' (1955) paper, however, the figure is much lower. For the BOAC flights Over the routes from London to the Far East and South Africa clear air turbulence was encountered in 18 per cent of the jet-stream cases. The same indication is given in a report by Riehl, Berry, and Maynard (1955) on the jet-stream investigations over eastern North America during the winter 1952-53. In their paper, these authors state that strong jets were virtually without turbulence, in spite of intense lateral wind shear, and that the re­ cord as a whole indicated only weak turbulence areas. Most papers containing statistics about clear air turbulence and jet streams give the percentage of positive turbulence reports in connection with a jet stream out of the total number of positive reports. Bannon (1951b) states that out of 296 reports 69 (23 per cent) were in connection with a jet stream, defined by him as a localized current with a speed equal to or greater than CLEAR AIR TURBULENCE AND THE JET STREAM 31

80 kt. In another paper (1951d) he has studied the corresponding figures for reports of heavy turbulence only and finds that of a total of 97 cases 69 (71 per cent) occur in connection with jet streams. Jones (1954) has the figures 147 and 105 respectively, i.e. 72 per cent. It ought to be pointed out here that all these authors have used differ­ ent definitions of a jet stream as no generally accepted definition was avail­ able to them. The question of determining the position of the turbulent areas with res­ pect to the jet stream has been tackled by Bannon (l951d, 1952) in the follow­ ing manner. For each individual jet stream a horizontal length unit was de­ termined to be the distance from the jet axis to the point on the low pres­ sure side where the wind velocity at the level of maximum wind had decreased to half its maximum value. This distance was on the average 170-225 km. As vertical coordinate a logarithmic pressure scale was used, measuring the pres­ sure distance from the jet axis. Then, the coordinates for the turbulence locations were determined in this coordinate system for each turbulence re­ port. These reports were then plotted on a mean cross section through the jet stream (Figure 7.1). As can be seen from the figure, most of turbulent areas are on the low pressure side of the jet. Very few observations stem from the lower half of the anticyclonic side. No turbulence was reported near the jet axis. This is in good agreement with a statement made by Frost (1953): "Once in the jet stream, contrary to general belief, flying conditions are usually velvety smooth". In Figure 7.1 the average distance of turbulence reports from the jet axis towards the cyclonic side seems to be of the order of 100 km. Jones (1954) has applied Bannon's technique on a sample of 147 cases with heavy tur­ bulence. His result is in agreement with Bannon's findings. Jones gets 75 per cent of the· cases on the low pressure side and 10 per cent in the lower half of the anticyclonic side. The horizontal distance unit is in his case about 250 km, and the average distance of the turbulence areas from the jet axis towards the cyclonic side is of the order of 100-150 km. It seems to be well established that the clear air turbulence that occurs in connection with a jet stream is more persistent in time and more widespread in space than normal with this type of turbulence (areas of characteristic width 50-75 km, dimension unknown along wind direction, depth 2-3000 ft). Fur­ thermore, the relation between jet and turbulence seems to be more marked in cases of severe turbulence than in cases of light turbulence. So far, only wind variations in a vertical plane normal to the jet-stream axis have been discussed. As mentioned in Section 5 above, pronounced varia­ tions of the maximum value of the wind speed occur along the jet axis. If one studies, e.g., 300 mb charts with isotachs, one often finds marked areas of isotach concentration with a large gradient of the wind velocity also in the direction of the wind (see Figurre4.5, 5.2). These closed isotachs often move through the large-scale wave patterns, and may for example be found at one time west of a given trough and later on east of the same trough. When 32 CLEAR AIR TURBULENCE AND THE JET STREAM

studying the vertical variation of the wind velocity above a certain geogra­ phic point one may observe a large variation with time of the vertical wind shear even if the jet-stream axis is found above the station all the time. This special aspect of the problem of the interrelationship between jet stream and clear air turbulence has been discussed by Clem (1954). He states that most cases of turbulence in connection with a jet occur in connection with the passage of a velocity maximum. The stability variations related to the passage may also have some bearing on the OCCurrence of turbulence (for remarks on the sharp irregular vertical variations in wind speed which Clem connects with the turbulence, see preceding Section). Clem's observation has been substantiated in a study conducted by the U.S. Air Weather Service (1956). Chambers (1955) states that clear-air turbulence in its severest form may often occur near the "exit" of a well-developed jet stream, or in an area as­ sociated with a "fork" or "bend" in the axis. Special flights made in box fashion parallel to and across the jet stream (Clodman, 1957) have revealed that clear-air turbulence makes itself felt much more strongly when the aircraft is flying parallel to the wind direction, than when it is flying crosswind. Although this conclusion is opposite to that reached in an earlier study (U.S. Navy 1955), it was stated in that study (based on frequency analyses of accelerometer records rather than pilot's es­ timate of turbulence) that the records analyzed did not justify a firm con­ clusion. Clodman's results may explain some of the differences in incidence of turbulence noted between the other investigations cited above. The flights in some of those investigations were, for example, primarily conducted in such a manner (flying across the wind) that turbulence may have been minimized. The above brief discussion of the connection between clear air turbu­ lence and the jet stream shows the complexity of the problem. The turbulence seems often to be of a patchy nature and the number of observations is far too small. Moreover, the reports have to be of a more homogeneous nature be­ fore we can hope to see a theory of clear air turbulence be developed. At the present time, to judge by the differencesin approach to the problem, opinion Seems to be divided in regard to the basic question whether horizontal or ver­ tical eddies (or both) are involved. Aside from turbulence associated with the jet stream as such, topographic features. have to be considered in some localities. According to Turner (1955), clear-air turbulence over Great Britain appears in SOme cases to be clearly related to the topography; such turbulence is often distinguishable from, but may occur along with, standing waves due to orography. An example of se­ vere clear-air turbulence (Canberra aircraft at 40,000 ft turned upside down) occurring in connection with standing waves is given by Jones (1955). Basic vertical motions in the waves (which may be smooth or turbulent) range up to 15 m/sec, or more in some localities (for example in the lee of the Sierra Nevada of California). Although the occurrence of standing waves is not res­ tricted to the immediate neighborhood of jet streams (the waves being primari­ ly related to strong winds and stable conditions at hill- or mountain-top le­ vel), the strongest waves generally do occur in jet-stream situations (Jenkins CLOUDS AND THE JET STREAM 33

1952, Colson 1954). Turner (1955) and Jones (1955), as well as Radok (1954a), suggest that locally the turbulence associated with jet streams may be ihten­ sified by interaction with the orographic waves.

8. CLOUDS AND THE JET STREAM

It has been known for a long time that some close connection exists be­ tween certain synoptic features and the upper winds. Already in 1913 Hesselberg published an investigation into the movement of cirrus clouds, and the high mean values of the speed of movement of medium and high clouds as observed at Blue Hill Observatory in the northeastern Unites States were known early. These values were rather high for that time and at first were regarded as somewhat doubtful. Later investigations have shown, however, that the area under consideration is characterized by high upper winds (Figures 3.2, 3.3; for an interesting comparison of old cloud speed data with up-to-date mean charts, see Jenkinson 1954). When the concept of the jet stream was brought into meteorology it became of interest to investigate whether or not there was any connection between cer­ tain types of clouds and the jet stream. An investigation of this kind can be carried out in different ways, and in this section three different methods will be discussed. The first method, introduced by Sawyer in 1951 is a statistical one, which tries to take the conditions around many jet streams into account, using the position relative to the jet-stream core, entrance, and exit as a reference system. Thus, when using this method one is in principle not interested in the geographical location of the phenomena. The second approach is that of Schaefer (1953b) and Schaefer and Hubert (1955). In this case the observer is placed at a fixed location (mainly Schenectady in the northeastern part of USA) and studies the distribution of clouds with relation to jet streams that are passing over the observer's head. To a large extent this study is carried out with the aid of color photos and films. The third method may be called the pilot's method, i.e. a cloud study made by a pilot when flying in a jet stream. This point of view was discussed by Frost (1953, 1954), a pilot of the British Overseas Airways Corporation. The method of analysis used by Sa~~er and Ilett (1951) is described by them in the following way : "The period covered by the analysis was the year 1949. Occasions of jet streams passing over or within about 500 miles of the British Isles were noted by examination of the 300 mb contour charts drawn re­ gularly at the Central Forecasting Office. For this purpose a belt of approxi­ mately straight flow with a maximum wind speed (observed or geostrophic) at 300 mb of 70 kt or more was taken as defining a 'jet stream'. However, in order to see if the chosen lower limit of velocity had any effect on the results, the statistical analysis was also completed separately for those cases in which 34 CLOUDS AND THE JET STREAM the wind speed exceeded 120 kt. The axis of the jet stream, that is the line of greatest velocity, was noted on the charts for 1500 GMT each day, and the distribution of medium and high cloud examined in relation to this. "All available observations of medium and high cloud for 1500 GMT were analysed in relation to their position with respect to the axis of the jet stream. The present scheme of synoptic reporting does not make provision for reports of the amount of the medium and high cloud layers on all occasions. However, an estimate of the amount of both medium and high cloud was made on the basis of the total amount of cloud reported and the amounts reported in lower cloud layers. For this purpose it was assumed that the same proportion of the whole sky was covered by medium and high cloud as in the part of the sky visible through the low cloud. If the amount of low cloud was less than 4 octas and no upper cloud was reported, both cirrus and medium cloud were assumed to be absent. Occasions of 4 octas of low cloud or more and no medium or cirrus observed were not included in the statistical summaries. "In order to analyze the distribution of cloud in relation to the axis of the jet stream, the area around the jet stream was divided into eight sections as indicated in Figure 8.1. The area was divided first into bands parallel to, the jet stream and 200 miles wide, and secondly by a line perpendicular to the axis through its mid point, dividing the jet stream into two equal sections longitudinally from the entrance to the mid point and from the mid point to the exit. The letters in Figure 8.1 have been used to define the sectors in the tabular results." Tables 1 and 2 give the results of the analysis. From the tables we can see that the amount of cirrus of 4 octas or more are more frequent to the right of the jet-stream axis than to the left. According to the authors this distribution was slightly more pronounced with the stronger jets. Furthermore, the amount of medium clouds are slightly less in Sectors A and B. The frontal and layer types of cirrus are more common to the right of the jet-stream axis, while anvil cirrus clouds (type 3) are much more common to the left of the axis. These features were better developed with the stronger jets, according to the authors. Finally, the tables reveal very clearly that altocumulus cumulogenitus (type 6) are much more common to the left than to the right of the jet axis. On the other hand, frontal types of altostratus and altostratus castellanus were more common to the right of the jet stream. The above findings are in good agreement with the distribution of cloud types that could be anticipated from Figure 4.9. To the left of the 300 mb jet stream the cold air masses are deep enough to allow considerable vertical growth of the cumulus clouds, while most of the upgliding motion OCCurs in the area to the right of the 300 mb jet stream. In most cases with a well defined limit of an area of cirrus clouds, this boundary lay near the jet-stream axis, and this was particularly the case when the jet was connected with an active front. Jet streams over ridges of high pressure on the sea level chart were quite often characterized by small or no cloud amounts in all sectors. The statistical study discussed in this paragraph has some shortcomings that reduce the value of the analysis: (a) It is difficult to place the exact CLOUDS AND THE JET STREAM 35 center of the jet stream with smaller error than about 300 km in the area under consideration. (b) The exact amount of medium and high clouds was some­ times difficult to evaluate because of existing low clouds. (c) The reports of the amount and type of the medium and high cloud are uncertain. (d) It is reasonable to assume that the cloud observations are more representative for the central portion of the jet stream, longitudinally speaking, than for the exit and entrance regions. (e) The investigation is restricted to a certain geographical area and the results are strictly applicable only to this area, their applicability to other areas depending upon whether the main features of the jet stream (e.g. vertical motion pattern, moisture, stability) have a general application or not. Finally, (f) the number of individual jets and the corresponding number of cloud observations are not given. In his first paper Schaefer (1953b) describes four different types of high and medium clouds that according to his observations show high correla­ tion with the existence of a jet stream aloft. The four classes of clouds (see original article for examples in color) are: 1. High clouds (type 4 and 5); cirrus streamers of great complexity moving at high velocity and showing long tufted streamers, complex shear lines, and massive whorls (illustrated by Figure 8.2). 2. High clouds (type 9); cirrocumulus in blanket-like masses scattered in a random fashion although sometimes in a line showing evidence of being at the crests of undulations in the stream. Clouds sometimes changing in character, shifting rapidly to cirrus streamers or showing fine structured waves at very high altitudes; some blankets show high order Tyndall spectra in green, red, and other colors when near the sun (illustrated by Figure 8.3). 3. Middle clouds (type 4 and 7); altocumulus lenticular wave clouds sometimes in great profusion with large lateral dimensions in the direction of flow of the stream; often with considerable vertical depths and piling up in many layers. Such clouds show little apparent relationship to ground topography, although they are basically "standing" clouds and, therefore, do not exhibit rapid movement except when snow is shed from them. When this occurs, long ·streamers may extend downwind for many miles to emphasize the high velocity nature of the air. When near the sun high order Tyndall spectra colors are commonplace (illustrated by Figure 8.4). 4. Middle clouds (type 3 and 5); a billow type cloud which may extend from horizon to horizon with the waves in parallel bands at right angles to the air flow. At times the cloud sheet may appear as a relatively thin layer with the units more cellular in form (illus­ trated by Figure 8.5). Schaefer gives a preliminary rule of thumb method for the detection of a jet stream from cloud observations made at the ground. If three of tha cloud types described above can be observed and there also is evidence of high velo­ city movement and coherency, then a jet stream is likely to be in the near proximity of the observer. If all four cloud types occur, Schaefer considers the evidence complete. So far no discussion of the distribution of the clouds with respect to the jet-stream axis was made by Schaefer. In the next paper (Schaefer and Hubert, 1955) such an attempt was made. In this paper Schaefer and Hubert try to find an explanation fo~ the "turbulent motion" cloud types which have been observed in connection with jet 36 NAVIGATIONAL ASPECTS OF THE JET STREAM

streams, and 'their position relative to the jet axis. The fact that the ver­ tical compOnent of the absolute vorticity often is near zero or at times acquires negatiVe valu'es to the right of the jet axis, looking downwind, is combined with the known distribution of the Richardson's number (Figure 8.6). Now, if the large-scale distribution of the vertical velocity is such that the' air on the high pressure side of the jet stream is brought to or near to saturation, the onset of turbulence as indicated by low Richardson's number may give rise to sOme of the specific jet stream cloud types as are discussed earlier. It is interesting to notice that according to Figure 8.6 the pre­ ference for these types of clouds is to the right of the jet axis, in good agreement with the findings of Sawyer and Ilett. The cloud pictures in Fig­ Ures 8.7 and 8.8 were taken at Schenectady, whose position is indicated in Figure 8.6, near the time of that section. Schaefer and Hubert mention in their paper that some indication ,of a rol­ ling motion about horizontal axes have been found in lapse-time photographs of jet-stream clouds. This type of motion was postulated by Rossby (1953) for narrow oceanic currents. In an article published in 1953, Frost gives two interesting examples of jet-stream clouds. On one occasion he was flying at about 5500 m and 3000 m below a narrow long cloud streak; While flying under the cloud he experienced a wind of 138 kt, exactly in line with the cloud streak. At another occasion he flew with a dead tail ~ind of 148 kt for about 2700 km directly under a thin cloud not more than about 2 km wide. In a second article (1954) Frost gives a third example of a narrow jet stream-cloud extending over large distances downwind. A cloud at about 6600 m was observed to reach from horizon to horizon but was only a few km wide. The cloud was observed to move eastward with a speed of 180 kt. On the same occasion Frost observed that the cloud had a 'well-defined edge on the pola~ side. This ,is in agreement with the findings of Sawyer and Ilett. Finally, Frost gives indications that a line of cirrus cloud paralleling the jet stream had a rolling motion ofa clockwise nature when viewed downwind. This note is interesting because it is in agreement with the statement by Schaefer and Hubert discussed above.

9. NAVIGATIONAL ASPECTS OF THE JET STREAM

In this section, a brief discussion of some special aspects of the jet stream is given. No systematic scheme of how to fly in a jet stream can be given in this general paper. Most of the facts that will be brought forward here have been mentioned before in earlier sections, more or less explicitly. The related problems of clear air turbulence and clouds in the jet-stream area have been covered earlier. Already in the early days of aviation history jet streams have upset operations. The number of such incidents was, however, small because of the NAVIGATIONAL ASPECTS OF THE JET STREAM 37 low ceiling of the first aircraft. In a paper by Durst and Davies (1949) a cas~ from World War I is mentioned where a German zeppelin air raid on the British Isles was hampered by the existence of strong upper winds. When the ceiling of aircraft increased, the number of jet-stream inci­ dents grew larger. During World War II it became more and more common that pilots and navigators reported very strong upper winds, and eventually me­ teorologists had to face the difficult problem of forecasting upper wind speeds of 100-200 kt or even more. Some figures quoted by Jacobs (1955) may be of interest to illustrate the difficulties; a local decrease of wind from 200 to 72 kt during 3 hours at 12 km, and a vertical increase of 150 kt in 900 m. Practical operations have belied the opinion held earlier by many, that use of faster aircraft would make the influence of the wind less import­ ant. On the contrary, an accurate knowledge of the wind field is critical for the economical operation of such aircraft on long-distance flights (for a specific example, see Great Britain Meteorological Office, 1955). The general question of forecasting upper level winds for aircraft has been discussed in great detail by Durst (1954a, 1954b) and by Rutherford (1956), who point out that there are navigational as well as meteorological limita­ tions to the accuracy to be expected in utilizing wind forecasts. No attempt can be made here to summarize the general navigational aspects. For the pilot-in-command and the dispatching organization the question is: Will there be jet-stream conditions during flight, and if that is the case will it be a head wind or a tail wind? If it is a tail wind the question is how to find it and stay in it during flight. In the case of head winds one will try avoid the jet-stream core, and if one happens to strike one, the prob­ lem is how to get out of it quickly. We will first deal with the above ques­ tions for flights well below the jet-stream core, that is on an average below 8 to 10 km. The value of a thorough pre-flight briefing cannot be over estimated. If the pilot and the flight operations officer can get an accurate view of the flight conditions well in advance of the time of departure, much is to be gained. The overall weight of the aircraft is predetermined, and every kilo­ gram saved in fuel weight means more paying goods, either passengers or freight. Furthermore, it is very important for the pilot to get a hint of the dif­ ferent possibilities of development of the upper air currents. If the fore­ cast goes wrong it is very helpfUl for him to know which direction the develop­ ment may have taken. Let us take one example·: A forecaster is basing his upper wind forecast on the assumption that a frontal wave will develop into a major storm that will be near the flight path of the aircraft, and has in­ formed the. crew of this assumption. Now, if the navigator during flight finds out that the actual winds are much weaker than forecast and he· at the same time can see that no heavy cloud system can be found, he knows that it would be useless to try to chase strong winds in that area. When in strong tail winds, it is the goal of the navigator to keep the aircraft in the jet stream if possible. If the flight is undertaken at a level 38 NAVIGATIONAL ASPECTS OF THE JET STREAM

below the jet-stream axis, then the aircraft thermometer can be used as a wind indicator (Davis, 1954). As can be seen from Figure 4.6 or 4.9, an air­ craft flying downstream in the maximum winds will have strong horizontal tem­ perature gradients on its left side and weak gradients to its right. If the thermometer readings, which ought to be taken every 10 or 15 minutes, using a vortex thermometer, show that the ambient temperature is rapidly falling off, then the aircraft is flying in rapidly decreasing tail winds and ought to make a right turn back to higher temperatures. On the higher-pressure side of the jet stream, the horizontal wind shear is smaller than on the left side. Thus, if the aircraft is misplaced towards the high-pressure side with regard to the jet core, it will not experience such rapid falling off of the tail wind component. The navigator can in this manner keep the aircraft in high tail winds with the aid of the thermometer. As a first approximation, in searching for the jet-stream axis, some help can be derived from the tendency for certain particular temperatures to be associated with the warm-air side of the frontal zone where strongest winds are .found. McIntyre (1955) found that over southern England there is a strong association between the jet axis and a 500 mb temperature of -22°C; Sorebreny (1955) states that between about 500 and 350 mb in winter over the southwest Pacific the warm-air boundary tends to be found at temperature 2-3° warmer than that of the standard atmosphere (standard is -21°C at 500 mb). McIntyre and Lee (1953) find that in winter over North America the strongest associa­ tion of high winds at 500 mb occurs with a temperature near -22°C ("maritime arctic front"), with other maxima near -35°C ("continental arctic") and -14°C ("polar front"). To fully utilize in-flight searching techniques, it is ob­ viously ess~ntial for the aircrew to be thoroughly familiar with the typical temperature and wind structures to be expected in the particular locale of their operations. The problem of keeping the aircraft out of strong head winds is handled along the same lines of reasoning as discussed above. If the head winds are too strong a right turn (Northern Hemisphere) through the area of strong cy­ clonic wind shear is made and is reflected by rapidly falling ambient tempera­ ture. At levels well above the level of the jet~stream core the same techniques may be used, noting that the strongest wind is at the cold, rather than the warm, boundary of the zone of the strong temperature gradient (Figure 4.9). It must be remembered that in this region the horizontal temperature gradients quite often are smaller and that the existence of the tropopause makes the conditions more complex at these levels. At about the level of the jet-stream core the thermometer readings are of no value for keeping the aircraft in or away from the maximum winds, because of the absence of a horizontal temperature gradient. In these areas the D­ value (deviation from standard atmosphere height, obtainable over the ocean as the difference between radio- and pressure-altimeter readings) can be used with·success. The D-value, which naturally can be used at all levels, can give an indication of the wind speed; a rapidly changing D-value during flight NAVIGATIONAL ASPECTS OF THE JET STREAM 39 means that the aircraft is crossing a strong wind zone. An aircraft flying downstream in high winds should maintain a fixed D-value as long as possible, whereas an aircraft in strong head winds should veer right and continue as long as the D-value continues to decrease rapidly. From 255 maps over the United States during the period August-December 1951, Fletcher (1953) found that in 92 per cent of the cases the axis of strongest wind was found, at 500 mb, between the contours 18200 and 18800 ft (-100 to + 500 ft D). The above discussion is based on the assumption that the aircraft is to be held at a fixed level and is able to search out other wind speeds only through horizontal movements. This is the case when the flight level of the aircraft is determined by an air traffic control service or when the perform­ ance data of the aircraft fix a certain altitude and temperature. It goes without saying that the most rapid change of wind speed may be effected usual­ ly by changing the height of the aircraft, since the vertical wind shear is about two orders of magnitude larger than the horizontal shear. The above general rules of how to deal with some navigational problems in jet-stream conditions can be systematized in different ways. One method, used by an airline flying between Tokyo and Honolulu, is discussed by Stiefelmaier (1955) and Serebreny (1955). A number of predetermined tracks between Tokyo and Honolulu are made up beforehand, and the forecaster and dis­ patcher choose one of them before departure and recommend it to the pilot-,in­ command. The pilot follows this track and makes adjustments to it according to the general rules indicated above. A correction to the upper wind forecast may be made as a suggestion to the pilot to switch over to another of the predetermined tracks, the decision often being made on the basis of temperature readings and other information sent to the forecast office while the airplane is en route. This method of correcting a forecast imposes very little burden on the communication channels. In Stiefelmaier's paper, the savings made to the company by using the jet­ stream flight techniques is said to have been half a million dollars on about 220 flights. In the Pacific, the jet stream on this particular flight is used on a regularly scheduled basis during the colder months, November through Marc~ In addition to the above-mentioned rules for jet-stream navigation, some of the findings discussed in Section 8 may be used. Sometimes special cloud formations can be found near the jet stream, and a pilot may be able to keep in strong tail winds by following a cloud streak for many hundred miles (Frost, 1954). Furthermore, the region of strong horizontal, cyclonic wind shear is some­ times the site of clear air turbulence. An aircraft flying in strong head or tail winds and experiencing clear air turbulence has almost certainly left the area of strongest winds towards the low pressure side. Finally, one ought to mention some facts that unfortunately reduce the value of jet-stream navigation. The rapidly increasing air traffic volume makes it necessary to lead the aircraft in certain corridors (airways) which 40 NAVIGATIONAL ASPECTS OF THE JET STREAM they are required to follow. This reduces the possibility for the pilot to take advantage of a jet stream by choosing another track. The airway system is becoming more and more common. Moreover, particularly with jet aircraft, it is not always most economical of fuel to fly at the altitude of maximum utilization of winds, or to expend the extra fuel required to adjust the flight path to such an altitude or location (Kelly and Caster, 1954; Reiter, 1957). Another drawback is that the customs officers and the people coming to the airport to meet a guest or relative don't like to find the aircraft two hours ahead of schedule! FIGURES 2.1 and 2.2 41

,.. 10". • . Fig u r e 2.1 Mean cross section, 0300 GeT, 30 November 1946, showing average distribution of geostrophic west wind (thin solid lines; m/sec and mi per hr) and temperature (dashed lines, oC) over North America, in a case of approximately straight westerly flow. Heavy lines, tropopauses and approxi- mate boundaries of barocline layer (Palmen and ~agler, 1948)

Fig u r e 2.2 Contours (solid lines, feet) and isotherms (dash9d lines, oC) for the 300 mb surface, 0300 GCT, 30 November 1948 (Palmen and Nagler, 1948) 42 FIGURE 3.1

c ... III,. • ~ , ...... 10 • "' • • 40 • .. l! .. • CO .. • .! 4' ~ ·e I• "- .. "- c < ... .. • "' ~ , 101 , c.

0

~

•.. .'

• --_---l0• • , I10d"S•II0d'S

Fig u r e 3.1 The normal zonal circulation (mean zonal wind averaged over all longitudes), in summer and winter for both hemisphereso Isotachs in meters per second. Mean easterlies stippled (Mintz, 1954) SOOW 400 E J400E Soow --;;-;;r--- _. i4O'

~~6QON

400 N

200 N 71 H gCl 61 0" m .w rv 20·$

'.448,

-~'"'+"'DOO 4<1'5 ~B!!­ ~-l-isir~-i-.J&400 -- ~"" IIIII- l-r

~--

Fig u r e 3.2 Streamlines and isotachs (kt) of the average vector wind at 200 mb in January (Jenkinson, 1955)

t; 800 W 400 E 1400 E 80DW 'II" 40" s:r _ aD" 100" -12t1' ~lL------.i!l~811' __ Hilt 14ll" 120" t .1 II

IO~ ~~--r~4-=---~---' .;., ~~~j. "~II' ----- ~ -- ) ., ",,-----t , .._ _ _ V ':>----"~ 'AO

---,"-;~ --- .. .. - .._. - .... 1~~i~~~~~~i~~~f-~[::>h~L...... ,~.::.::1. ~ I ,",0 . .~ 40"N >-.'"..c::::i-o-::;y-0z,g.-<,,~,~ - ~~ / 7j H Cl ~ h1 .W W

,

r··-- 1r \ d'l r, mo'W- 14i 'Ii "

Fig u r e 3.3 Streamlines and isotachs (kt) of the average vector wind at 200 mb in July (Jenkinson, 1955) FIGURES 3.4 and 3.5 45

r------,--~Z~O~N~'~L~.~,~ND;;---T------'KM I-_J_A_N_U_A_R_Y +-_e~o~.~p~O~N~ENT"'_'.~IN'_'K~N~OT~S'_____1------1-"""""130 -10 mb -20 :..··115 ···

-100

-200 10 -300 -eoo -700 -1000 0-

-1000 O' 9O'N 60' Fig u r e 3.4 Zonal corr~onent of mean flow (kt) at meridian SOoW. Easterly com­ ponent indicated by dashed lines (Kochanski, 1955)

70 I 10 ~ 5_ ~ LAT "- O \ /' ""--E- \ ..... c 0 60 I / - __ ---5 / 10 5~ 10 20 _25 50 ~ ... "" 30 ~ 20 / / ~ 4() --

~o 10 ,.--.... , '" ...... ---___ 30 " , ~- 20 o ..... "----__ -25 /~-E-- ..... ' ' ..... 20 -5' , 10 -5, ---- ..... 10 .....--~-J"U"LvY~~A..U"G''-''"SE''PT>r.....'o1iiC''iTr...... 'Nllio\i:v,.L-''O'''Er:C-'''--..,J;;;A1ilNr'----' Fig u r e 3.5 Seasonal distribution of zonal flow Cm/sec) at 300 rob, July 1945 - January 1946. Heavy solid line, maximum westerlies (Riehl, Yeh, and LaSeur, 1950) -!' ISOTACH ANALYSIS 200 mbs February 25. 26. 27. 28. 1956 0'

5 ~~~:~:~~~'~~i~~'iOO~i~~~~~~~OO~~~~':O:~~:~~~~i~~~~~~~j~~~;00;~;~;";;~:";0~~;~"~0~~;;"~0~~~~';"~~~~'''~~W~l'604S 00 :so":r..... S'"__50 ... ---..:::: -100!>o'" loo!& s 30

.-- -- 100 ~ 100 :"'--__..5lJ- __ ~ _ :;0 ~n ~ ___-""''l:l';;;~ 151 ~ , v, " O,iO "i2O eo 0 "" '00 " " ," '00 'BO '60 'f·~ ~ 'ZC' '0;) ~. Br:>.60 40 20WOC20_!Vl~ 80 100 IBO W 160 .. ( JF@5 !{ v F::J .--..... '"0-.. S~ ~

3pl ~ ~\00 S j" _50--::::~1 '00 l::=1Q9=---~ "-00 ~_IOO-- _ 50( '5~ __50-- + J " >n H 0je::c ~ '';0· 0 '20 " " N " 40 "i4O • '" '" w "i60 Gl '00 " " §3 m w oo~"""O ~:OO~ " 0' ~~~~::~~,,;o~~~~,~00~~i;~~~~"0~~~'~o~~~;,,~;~~~~~~,~0~~~~'~O~i~;'~O~:::'~O:~~~";O~~~~~~~~§~~:'~"~:~~':"~~'L_']OO"0 00 "I'30 5h...... ~ 150 ... ::...-=-~~--__"'__ 150 ~('00 ( ..+ S _oo--.::-_~- '00-""," - " "'" "'" "O~"'--~ ,:;1'""-_,00- - >or =:::-..z: __50:' __-r + + + \. ... \ / "

°i~o IW 80 .., N N .., '" '00 " " " T20 '" '" iOO 160°

oo~'OO" " '" '00 " " ",," W 0 , " '00 "0 ," '00",- 30 ~.... 4=- ~ 50 150~~ ~o ..... /') ./"" iF »f' ~ 100 ~ l--$O-...... '" so~ _"",,.- _- 0 1,~102-' _- _...... il .. ~. ~ 15 --100-":.--- .. ~.... ------• " ~ ~ ! \ ) / \'Ai d' \=r'l I0 o ...a 120 100 eo eo 40 iW wOE 20 40 60 eo 100 120 140 IBO 180 W 160 Fig u r e 3.6 The subtropical jet stream as shown by observed winds and isotachs (speeds in kt) at 200 mb level, on 25 (top) to 28 February 1956 (Krishna Murti, 1957, to be published)

------~---~---~~~~~~~~~---~~--~--"~~~~~~-~.~------~.. ~-~- FIGURES 4.1 and 4.2 47

FEBRUARY 6, 1'352:, 0300 GCT ~-,,-- "'"

Fig u r e 4.1 Temperature distribution (oc) at 500 rob, 6 February 1952, 0300 OCT. Heavy line marks ap_ proximate southern l~it of polar air including frontal zone (Bradbury and Palmen, 1953)

50

., ,', f -50 ': ... .. (::'.:. ':"':':' .. '. I . :: .' .. .::...

50 ". '"L-;l>-."'i>-'70l>---.l,-----;l>-'.,--,(n'o Milo per Hour Fig u r e 4.2 Average latitude and speed of jet streams at 300 rob, for July-September 1945 (left) and October-December 1945 (right). Each dot represents mean speed (abscissa, roi/hr) and lati­ tude of jet axis (ordinate) for one day. Data represent 270-degree sector of Northern Hemisphere from 1100 E eastward to 20 0 E (Cressman, 1950) 48 FIGURES 4.3 , 4.4 and 4.5

Fig u r e 4.3 The jet streams associated with a cyclone family. Thin lines, sea-level isobars; wide lines, schematic jet stream (Vederman, 1954)

Fig u r e 4.4 Winds and isotherms (interval, 2C) at 500 mb, 13 November 1951, 0300 GeT. ~ Axes of minlinum and maximum tempera­ ture gradient are marked with dashed lines. Heavy dot in central United States marks surface low pressure center (Riehl and Teweles, 1953) '0

Fig u r e 4.5 Isotachs (interval, 20 kt) at 300 mb, 13 November 1951, 0300 OCT. Heavi lines, jet 5 tream axes; precipitation area hatched (Riehl and Teweles, 1953) FIGURES 4.6 and 4.7 49

40

--+f---+---+cY'7----;'\-+---'50

" = , 850 Fig u r e 4.6 -, , -- , , , ,i , , "XlO Vertical cross section normal to jet stream, 768 576 476 276 1500 GCT, 3 April 1950, in region where dis­ GGW lND OJT PHX tinct polar-front layer was present. Wind 1500 GeT 3 APRIL [950 = ,=~ speeds in knots (Newton, 1954) , I

;55 60 , 40... _- 40 60 (LCXXlmll",,) "'0m" " -50'-

40 , -45/ ''''' - -60

-6 20 "'" --55 ___50 _ -45 300 -<0 --:35 --30 --25 _ -2.0 • - -15 " --10 - -, --,--0 " -OQ roo -" -,- "''' 20, '20 , , 20' - '000 764 662 450 eo, 265253 F i 9 u r e 4.7 BIS RAP '"LB' DOC '"OKC FW BGSSAT m Cross section at same time as Figure 4.6, at 1500 GeT :3 APRIL 1950 , ,=~ location 500 kIn downstream (Newton, 1954) I ':" I 50 FIGURES 4.8 and 4.9

""" 00 .. ~ ------r----'-;.!~!!L------oo , ' IODEGI950 . 03 GeT -=-='::':--I--j-/.~~--;:;::;::-'''' ...... COlD 51)-- -40- •...... '" 2---,---", K·-·eo

- ~50 200

Fig u r e 4.8 Cross section over Japan from Wakkanai to Iwo Jima, 0300 ceI, 10 December 1950. Speeds in m/sec (Mohri, 1953)

Fig u r e 4.9 Cross section from Hannover to Valentia, 9 November 1949, 0300 OCT. Isotachs are for observed wind speeds in m/sec (Berggren, 1952) FIGURES 5.1 , 5.2 and 5.3 51

\ , , -1350 /' • , .., - ro , 1\\ ,.• 3ZO )340 i£ ,\\ ,.. --""r+1-tt-MI-fl,It:I:tf1'f:?®lJJffI-t+--tff-', . \\\ " , . '.I. , I iii J -. -_.:::...... ~ };no ,. ,,- "'-- --> ",. , -', ' ~ ,~;:- " ,,- .. "- \ .I:'.. , ~ ,." ,/"",'" '/./ ,,----:c- " \ ~ ~- -320 / ':--' , ---- -, ~, ""/ , ~------....:: -"".- ~ .... , -....:: I 290-­ ", -~ ~----- , , -' "- ----= i i to 00 ~-"i-,--,,,t,"-+,-.";,-",'---,1-,, !>O 4~ •0" ,.. AMette Island Ta:toosll Spol<_ o 500 IOOOkm ~~gs~dr9 f-I~~+I ~.~~'-11 4 ""1 Honj?'----;"'..-_. Fig u r e 5.1 Fig u r e 5.3 Profiles of geostrophic zonal wind speed (m/sec) Vertical section through three jet at various isobaric surfaces (labeled on curves) streams, 1500 GeT, 4 August 1949, be­ for an average of 12 cross sections along 800 W tween Annette Island, Alaska, and Las in December 1946. Dotted line indicates inter­ Vegas, Nevada. Wind speeds in knots sections of frontal boundaries with wind pro­ (Newton and Carson, 1953) files at various isobaric levels (Palmen and Newton, 1948)

Fig u r e 5.2 Contours (ft) and isotachs (kt) at 200 rob, 25 October 1950, 0300 GeT (Rossby, 1951 b; analysis by B. Bolin) 52 FIGURES 5,4 , 5.5 and 5.6

roV (m/sl,

! I r" ·...... 1

1 j - •... ----r":4~ i : :1:,,' : . : ! i ! ,-.....".-'-1' i,' j ,i---~...~-! : _.- -- • &-_g;;;f<"<~"_..e • • • Fig u- r e 5.4 Fig u r e 5.5 Profile of jet stream over British Isles, 1 Septem­ Composite diagram showing wind-speed ber 1952 at 300 mh. Solid line is profile as deter­ profiles (m/sec; ordinate units are mined from frequent photographic fixes (Hurst, 1953) hundreds of km arbitrarily placed) for 5 Navy jet-stream flights plus that by Hurst (Figure 5.4) (Riehl, Berry, and Maynard, 1955)

mb ------/

1800t

4" ,.. 31" ...... 34'

Fig u r e 5.6 Cross-section analysis of wind speeds (kt) observed by a B-29 aircraft of Project Jet Stream, U.S. Air Force; 2 traverses between Atlanta, Ga. and Milwaukee, Wise. at 280 and 380 mb. Dashed lines, isotachs from conventional network at 1500 GeT; times of aircraft traverses indicated in figure (Landers, 1955) FIGURES 6.1 and 6.2 53

Octant 226°- 2700 ... Radius 0.0 - 3.9 Deg. Lat. , ... ,, ...... , N-9 I'----- '- ...... r--...... o ...... r--...... """- z ... " ~...... - f- __.. r-.... l­ .... --- r--:I-.. .. I."z --- I ~ "' "," 1____--- o 1---- ::::- ., -- ~'" z 1,.-- -- V L,....- ",'" ",' -- '" - L--- ~- V "." g , / ~ --" z '" ------1/1_...... --- .2 .3 :4 .5 .6 .7 .8 .9 1.0 WINO/l.tAX WIND Figure 6.1 Approximate mean distribution of wind speed with height in vicinity of jet stream. Ordinate is height in thousands of feet above or below level of maximum wind. Abscissa is ratio of wind speed at a given level, to the speed of the maximum wind. Solid curve is mean; dashed curves show variations about mean (U.S. Navy, 1955)

,001~-~~.-..---r--.,--r--'-"-T--r-,--'00

mb \~,. mb

I~~1 ---l----A---:.''----,.\-P-c---::'::"::j-o-d-----t--+-1--+---+--1~ _L.L~-l-:·-:·E-~·t-~:~j·JS--·---I:=:tj::=:kdbl '00L ...... ~ "~-~" -~.~-~..,..;"" """ ,_ • ",'...... -,...... " t.:::--- ...... ,~~~~ -~-"e:-:~ r- - .--- e::.- L-:: ~~..- ::. 1 jL.---:--- ._.- -;:.:___ ,00,~---t:=;~#:"a9'~=f::::;;"'''''--T--r---t--t---j--l'OO I r- ..... r n~ pUM i _._. )/ ...­ l,oo)I-+'-1A~·'rc---+!---+-~+--+--i--.J.--+--+--i--j.oo 1 i./\ \ 'oo'I-l--"l]\t--"t--'I---+--+_-+_-..I__L_...L_...J._-..IL-j500 ,_ ..fl,J' -----... Nashville 1500 GCT 9.Jull 1950 600)~.j.1~'''i.'-I]''"';LJ--+__+-_--+__ ~~=~.: ~~:~~~~I~~s o~~o G~~T 2::j~~li ~~~~ I~ Siewart Field {West Poinll 600 "f: .~ 0300 GCT 27. Mal 1948 ~. I ~ .". ...--...._..... ForI Wartll 1500 GCT 2.Junt 1948 ,00f-+-.:'-!-4""::j.---+--+---+--,-,,.-,---,._--,_...... j,00

o 10 20 .0 50 60 10 ao Knoten 90 '00 110 Fig u r e 6.2 Variation of wind with height in some cases where the strong winds were confined to a shallow layer near the tropopause (Rossby, 1951 b) 54 FIGURE 6.3

90 , , ' ,--'' --- -60__

-6~__ eo -'0-

70 ...w -4$ w 50 , ~ .1.. ~ ,, 0 , '"0 ..,. % , ,, .. w , 60 '"=> , 0 => ... , '" , ...", '"w ... , ... '".. Ii... ,• " 100 .64 r -'0 I .45t , '"W ,,I " ,• 50

_471 ~44~ 150 , ,• , : , , ~'H ,, \ • 40 200 L... ." , ." .... ,, ,

082 202 9'7 924 072 0" 968 964 250500GCT

Fig u r e 6.3 Vertical cross section from Alert, northern Greenland (082) to Whitehorse, Yukon (964) in a line from NE (left) to SW (right) across northern Canada, 1500 GeT, 26 February 1956. Tropopause is thick solid line near 300 mb (at bottom); thin solid lines are isotachs (kt); dashed lines, isotherms (oC) (Lee and Godson, 1957) FIGURE 6.4 55

20

// // / / 18 / 16 ------// 14 /

/ / 12 -...... E ...... ~ , 10 :c -- ";;;'" :I: 8

6

4

2

20 40 60 80 100 120 140 160 180 V - knots

F i 9 u r e 6.4 Radiosonde observation at Washington, D~C. on March 14, 1954, 2100 OCT. Thin solid line gives wind-speed profile as originally comput­ ed; heavy solid line is smoothed profile; dashed line shows profile drawn using teletype reports (Reiter, 1957) 56 FIGURE 7.1

mb. ~-1601--11--~----,---r------r---....., I . PJ-140r----t-----t---+,---+----+-__-1 --- ':I- 110 ~----- ...... , 'I-- ,,\ ",...-- -- ...... '...... \ \ :,..-/ F---, '..... 'I' \\ F3 - 80 - -'- - - '\ \\ /' ...... 14 \\ ./ ,,- ... r-- , ~~'" I • \ ~- 50r--~f---j--+I-_+-_=Hf__--1'H~~:;l~'·~·'...:.\41+-\\------1\,---\-\-l---I1-----1 \ \ ("- ~ \~'\ \ \ \ \\ ().) ',\ \\- \. 1. \\ II\ c. ", ''\j '\ \ \~, ~ I I,I J PJ " ", I'" \\ II ~ "\"' 90 I I I II I <;) '\ '\ 50 ' ...... ~,' I I,I ...;+-__ ,I d: f3+50 " "... '\ 'Jo. " ...... r: "I ,'I' " )0 " ~ I ,' , ,,'...... v,// I I' f3 +11'V'Ul...1----'----'t~--='--.,.----1-----=-:..=.=-·-f/----;A',/.'-=."WI~~-;iL_i__/-i----__l 50 ", V'/ ;tl~ It // ~ /1)/ / ~ +150r..:..::...... ,::--t-~'~-lr_+------Y...:..-~·C-.--_tJt______;f--_l---_lr- ' " "" / -40,'...... , -/ I~I. / " // I - / II AnricycloIhie - ...... - ~ ,/ 3d 20 Low-pre5SUr12 ~+250i---=s_i d_e_;;- T-__-----:!;-~/__~iI __!I:-=s..:..id_e:....--::! -3 -2 -I 0 Z;3 Horijonl-al disl'ance -- -Isopleths of wind veloci~y • Isolaied observalion of lurbulence normal ro sedron (pereen~age - Observation of ~urbulenc12 of maximum) along a line _ tv1iZan rropopause surface CJ Zone of observed rurbulence

Figure 7.1 Composite cross section showing clear-air turbulence reports plotted with respect to jet stream. See text (Bannon, 1952) FIGURE 8.1 57

A E ~ o B F lil j J.r-5~,.am axis ,------~ ~ C G ~ t

1g o H 'l' Fig u r e 8.1 Sectors about jet stream used in study of cloud distributlOn (Sawyer and Ilett, 1951). Tables I and II are laid out in same format as this figure TABLE I Sector Cloud amount (oktas) Total No. Sector Cloud amount (oktas) TotalNo. a 1-3 4 5-7 8 of obs. a 1-3 4 5-7 8 ofobs. percentage~requensv percentage frequency MEDIUM CLOUD A 38 23 17 16 6 154 E 34 16 15 20 16 335 B 50 21 12 II 5 256 F 34 21 12 18 15 574 ~ ------...... C 30 25 15 21 IO 334 G 36 16 12 20 16 764 D 31 17 14 24 14 177 H 34 12 13 23 17 641

HIGH CLOUD A 37 44 12 6 1 95 E 37 46 10 5 2 205 B 45 30 16 7 2 201 F 58 27 5 8 I 308 ------...... C 22 49 19 8 2 192 G 31 35 18 12 4 458 D 29 32 23 II 5 104 H 29 36 '7 17 I 369

TABLE :IT

Sector Cloud type· Total No. Secto, Cloud type. Total No. , B I I , I 0 2 3 4 5 6 7 9 of obs. 0 2 3 4 5 6 7 B 9 of obs.

1 perunlagt frequency 1 percentage frequency MEDtUM CLOUD A 3B 2 6 7 9 2 26 9 I , '5' E 3. 5 7 7 , 19 13 , 0 335 B 50 2 5 co 7 2 14 9 0<' 256 F 3. 9 7 I 20 12 ,< , 57. ------•'." ----+ C 30 6 '3 " 2 B .. 3 , 33. G 36 5 9 <02 10 15 ,< , 76• D 31 •5 12 9 9 2 0 .. 7 3 '77 R 3' 6 "12 II " 2 • 19 , , 6., HIOH CLOUD A 37 9 15 23 5 2 2 2 0 95 E 37 15 22 , 3 4 2 3 2 205 B .5 9 9 '5 3 3 9 , •2 20' F 5B "5 5 '5 2 • 5 2 3 , 30B ------• ------'-+ C 22 21 17 B 2 5 10 6 5 192 G 3' 15 1.8 6 2 7 6 5 '5B D !l9 15 22 2 5 B 6 R 29 19 19 3 6 B •2 • 369 •7 • 3 <0' 3 5 5 ·International code figures as used in 1949 (see" Handbook of weather messages, codes and specifications ", London, 1949, Part II, pp. 20 and 21).

FIGURES 8.2 and 8.3 59

Fig u r e 8.2 Jet-stream cirrus (Schaefer, 1953 b)

Fig u r e 8.3 Cirrocumulus (Schaefer, 1953 b) 60 FIGURES 8.4 and 8.5

Fig u r e 8.4 Altocumulus lenticular (Schaefer, 1953)

Fig u r e 8.5 Altocumulus billows (Schaefer, 1953) FIGURE 8.6 61

mb mb ______---..;'0p'5'--"fo5'-YI.OL-__ 200 --'T-' _ 200

300 ----+-+--rr'1++-\--I--I-----+---,I---- 300

400 ------+-t+\r\-JrllitH+-+--+-t/'------400

500 ------\----''r--f'ti--\-~.,.J.--".\'-,I-+------500

600 ---,------,---""',-----'-,---- 600 N Jet 500km S Axis

Fig u r e 886 Vorticity analysis (solid lines, units are multiples of Coriolis parameter) in vicinity of polar front jet (axis indicated by J) in cross section from Goose Bay to Miami, 1500 GeT, 2 March 1953. Dashed lines, Richardson numbers 0.5 and 1.0. Hatched where Hi less than 1 and absolute vorticity less than zero. Location of Schenectady shown by arrow (Schaefer and Hubert, 1955) 62 FIGURES 8.7 and 8.8

Fig u r e 8.7 Cloud photograph at Schenectady, New York, on 2 March 1953, 1230 EST (173QGeT) looking E (Schaefer and Hubert, 1955)

Fig u r e 8.8 Same, toward N at 1645 EST (2145 GeT) (Schaefer and Hubert, 1955) BIBLIOGRAPHY

The bibliography to follow includes the bulk of papers to date on the jet stream. Although the foregoing report has been confined to observational aspects, papers on theory and forecasting, and a scattering of papers in areas more or less directly related to the jet stream, have been included in the bibliography. Because of the large number of papers listed, it is desir­ able to draw attention to some particular articles and surveys : 1. Extended discussions and surveys of jet stream and general circula­ tion : Eady and Sawyer 1951; Flohn 1950 b; McTaggart-Cowan 1950; Petterssen 1956; Riehl, Alaka, Jordan and Renard 1954; Rodriguez Franco 1955; Sheppard 1951; University of Chicago 1947. 2. Mean circulation; climatology of weather systems : Brooks, Durst, Carruthers, Dewar and Sawyer 1950; Gibbs 1953; Mintz and Dean 1952; Petterssen 1950; Widger 1952. 3. Analysis techniques on upper-level charts and cross sections, etc.: Saucier 1955. 4. Dynamic relationships between weather systems and jet streams, and weather forecasting : Dickson 1955; French and Johannessen 1954; Petterssen 1956; Riehl and collaborators 1952. 5. Analogies with oceanic currents, and hydrodynamics experiments : Riehl and Fultz 1957; Rossby 1953. 6. Aircraft operations: Bannon, Frost and Kirk 1956; Dwyer 1953; Harrison 1951,

Extensive bibliographies on the jet stream and related topics include the following: Jet Stream - Evans and Kramer 1953b, U.S. Air Weather Service 1952; High-level Winds - Evans 1953, Evans and Kramer 1953 a; Tropopause Rigby and Kramer 1954; Turbulence - Kramer and Rigby 1952. -

In preparing this monograph, great help was derived from the reference to Meteorological Abstracts and Bibliography (MAE). With few exceptions, all articles listed in MAE under the heading "Jet Stream" in Volumes 1 through Number 8 of Volume 8 (August 1957) are included; abstracts for other papers not listed under this subject heading were also scanned.

Papers are listed by author, year, title, publication, volume, and page number, in that order. Where an abstract has been located in MAE, the MAE index number follows in parentheses. Index numbers 1- to 12- are for numbers 1 to 12 in Volume 1; index numbers for other volumes are in the form 3.2- or 3B-, for Volume 3, Number 2; 6.7- or 6G-, for Volume 6, Number 7, and so on. 64 BIBLIOGRAPHY

To save space, publication names have in most cases been abbreviated according to the following list

Aer. Aeroplane, London AFSG Air Force Surveys in Geophysics, U.S. Air Force, Cambridge Research Center AMM Australian Meteorological Magazine AMGB Archiv fuer r'ieteorologie. Geophysik und Bioklimatologie AWSTR Air Weather Service Technical Report, U.S. Air Weather Service AWSM Air Weather Service Manual BAAlS Bulletin of the American Meteorological Society BDW Berichte. Deutscher Wetterdienst in der U.S.-Zone CPRMS Centenary Proceedings. Royal Meteorological Society GBMR Great Britain Meteorological Office. Meteorological Reports GBPN Great Britain Meteorological Office. Professional Notes GM Geophysical Memoirs, Great Britain Meteorological Office GPA Geofisica Pura e Applicata GRP Geophysical Research Papers, U.S. Air Force, Cambridge Research Center lAM Scientific Proceedings. International Association of Meteorology (UGGI). Rome 1954 IJMG Indian Journal of Meteorology and Geophysics JIN Journal of the Institute of Navigation, London JM Journal of Meteorology JMSJ Journal of the Meteorological Society of Japan JRAS Journal of the Royal Aeronautical Society MAB Meteorological Abstracts and Bibliography MM Meteorological Magazine MRP Meteorological Research Papers, Great Britain, Meteorological Research Committee MWR Monthly Weather Review NZCN New Zealand Meteorological Service. Circular Note NZTN "ew Zealand Meteorological Service. Technical Note PMG Papers in Meteorology and Geophysics, Tokyo PTMe Proceedings, Toronto Meteorological Conference, Royal Meteorologic­ al Society BIBLIOGRAPHY 65

quarterly Journal, Royal Meteorological Society Tellus USWB United States Weather Bureau, unpublished typescript

Wea o Weather Wwi. Weatherwise

*Aanensen, C.J.M., 1948 : Turbulence in clear air near a warm front surface. MM 77, 209-210

Aeroplane, London, 1950 : Research into clear gusts. Aer. 78, 237-238 (9-99, 3K-157, 5D-174)

Aeroplane, London, 1952 : Meteorology and Jet Aircraft, I and II, Aer. 82, 234; 285-286 (4.1-32)

Aeroplane, London, 1954 : Jet stream variations. Aer. 86, 228 (6.2-135)

Alaka, M.A., 1955: A case study of an easterly jet stream in the tropics. Univ. Chicago, Dept. Meteorology, Ph.D. dissertation, March 1955 (75 p. typed)

Anderson, A.D., 1952 : Meteorological trajectory study for test flights to be made from San Francisco. U.S. Nav. Res. Lab •• NRL Mem. Rep., No. 23 (4G-88)

*Anderson, R., B.W. Boville and D.E. McClellan, 1955 : An operational frontal contour analysis model. QJffiAS 81, 588-599 (7.3-167)

Arakawa, H., 1950 The conservation law about the horizontal of the total vorticity. PMG 1 (2.10-62)

* Referred to in text. 66 BIBLIOGRAPHY

Arakawa, H., 1951 Possible heavy turbulent exchange between the extratrop­ ica1 tropospheric air and the polar stratospheric air. Tel. 3, 208-211 (4.8-99)

Arakawa, H., 1951 Tropopause in a steady zonal wind field. JMSJ 29, 86-89 (3.3-112, 4G-58, 5D-177)

Arakawa, H., 1952 The anticyclonic eddies just south of jet stream. A~GB 5, 1-4 (3.11-113, 4G-89)

*Arakawa, H., 1953 Clear-air turbulence near the jet stream. QJm~S 79, 162-163 (4.6-140, 4G-120)

*Arakawa, H., 1956 Characteristics of the low-level jet stream. JM 13, 504-506 (8.2-127)

Aubert, E.J.; Clem, L.H.; Klein, W.H.; Winston, J.S.; Hawkins, H.F. and Martin, D.E., 1950-53 : Weather and circulation of ••• Nov., Dec. 1950; Apr., May, Nov. 1951; Jan., Apr • ••• Aug.; Oct., Dec. 1952; Jan• ••• Mar. 1953. MWR 78 : 201-203, 217-219; 79 : 71-73, 96-99, 208-211; 80 : 7-9, 70-72, 82-87, 99-104, 118-122, 134-137, 190-194, 246­ 249; 81 : 16-19, 43-46, 77-81 (3.6-7, 4G-121) (see also later monthly discussions in ~{wR)

*Austin, E.E., and J.K. Bannon, 1952 : Relation of the height of the maximum wind to the level of the tropopause on occasions of strong wind. MM 81, 321-325 (4.4-174, 4G-90, 5D-199)

*Austin, E.E., 1953 : Upper winds at Aden. QJRMS 79, 528-532

Austin, E.E., and D. Dewar, 1953 : Upper winds over the Mediterranean and Middle East. MRP 811 (2 p.)

Badner, J., and M.A. Johnson, 1957 : Relationship of tropopause and jet streams to rainfall in southeastern United States, February 4-9, 1957. MWR 85, 62-68

Baker, W.C., 1952 Riding the jet streams. Air Facts, N.Y., 15, 39-45 (3K­ 209)

Bannon, J.K., 1948 Meteorological factors in the occurrence of turbulence at high altitudes. MRP 436 (12 p.)

Bannon, J.K., 1951 a : Meteorological aspects of turbulence affecting air­ craft at high altitude. GBPN 104; MM 80, 271 (3K-162, 4G-60)

*Bannon, J.K., 1951 b : Severe turbulence encountered by aircraft near jet streams. MM 80, 262-269 (3.2-120, 3K-163) BIBLIOGRAPHY 67

Bannon, J.K., 1951 c : Severe clear air turbulence experienced at high alti­ tude on 2 and 7 November 1950. MRP 631 (3K-145, 4G-61)

*Bannon, J.K., 1951 d : Turbulence at high altitude: a further meteorological analysis. MM 80, 331-332 (4E-207)

*Bannon, J.K., 1952 Weather systems associated with some occasions of severe turbulence at high altitude. WA 81, 97-101 (3K-188, 5D­ 201)

Bannon, J.K., and N.E. Davis, 1953 : Atmospheric circulation at high alti­ tudes in the tropics and subtropics. MM 82, 116-121 (4E­ 249)

*Bannon, J.K., and M.P. Jackson, 1953 : Relation between tropopause and level of maximum wind at Gibraltar. MM 82, 100-102 (4E-250, 5D-219)

Bannon, J.K., 1954 a : Note on the structure of the high altitude strong wind belt in the Middle East in winter. QJffiAS 80, 218-221

*Bannon, J.K., 1954 b : Note on the subtropical jet stream in January and April 1951. IWA 83, 257-263 (6.2-127)

*Bannon, J.K., 1954 c : Some aspects of the mean upper-air flow over the earth. PTMe, 109-121

*Bannon, J.K., B.C. Frost and T.H. Kirk, 1956 : Some meteorological aspects of high-level navigation. (Three articles); Bannon: Strong winds in the upper atmosphere above 15,000 ft.; Frost: Jet streams and the pilot; Kirk : The problems of fore­ casting. JIN 9, 282-309 (7.10-49)

Bannon, J.K., and R.A. Jones, 1956 Average wind at 60 mb. ~! 85, 194-200 (7.5-191)

*Bassus, K. von, 1906-1907 : Ueber die Windverhaeltnisse in der oberen Inver­ sion. Beitrage z. Phys. d. freien Atmos., 2, 92-95 (5D-9)

Beamer, C.C., and S.M. Serebreny, 1953 : Pacific jet stream research, for the period 1 February - 30 April 1953. Fan. Am. World Airw., Inc., Pac. Alaska Div.; Bur. Aeronaut~oject AROWA, Contr. N189s-90981, Frog. Repo No.1 (41-279)

Bell, G.J., and L.H. Kwai, 1953 : Upper winds determined by radar 1949 to 1951. Hong Kong Roy. Obs., Tech. Notes, No.5 (4E-251, 5B-304) 68 BIBLIOGRAPHY

Bellamy, J.C., 1954 : Four dimensional flight planning. Navigation 4, 105-113 (6.7-91) Bergeron, T., 1954 Multiple frontal systems as links in the general atmo­ spheric circulation (Summary only). lAM, p. 289

*Berggren, R., B. Bolin and C.G. Rossby, 1949 : An aerological study of zonal motion, its perturbations and breakdown. Tel. 1 (2), 14­ 37 (2-74, 4G-13)

*Berggren, R., .1952 The distribution of temperature and wind connected with active tropical air in the higher troposphere and some remarks concerning clear air turbulence at high altitude. Tel. 4, 43-53 (3K-189, 5D-202)

*Berggren, R., 1953 On temperature frequency distribution in the free atmo­ sphere and a proposed model for frontal analysis. Tel. 5, 95-100 (5.2-146, 5D-242)

Berson, F.A., 1950 On the rale of long-wave instability in the general cir­ culation; a study of five-day means in November 1948. Sweden. Meteor. och Hydrolog. Inst., Medd., Ser. A., No. 3 (4G-31)

Bhalotra, Y.P.R., 1955 :A case of severe clear-air turbulence over north India. Wea. 10, 329-330

Bilancini, R., 1950 : La "corrente a getto" (the jet stream). Rivista di me­ teorologia aeronautica, 10(3), 3-13 (2.9-75, 4G-32)

Bindon, H.H., 1950 A preliminary report on high level turbulence above 20,000 feet over Eastern Canada. Nat. Res. Coun. of Canada, Report, No. C.C. 125, 6 p:-T4E-182)

*Bjerknes, J., and E. Palmen, 1937 : Investigation of selected European cy­ clones by means of serial ascents. Geofys. Publ. 12, No.2, 62 p. (4E-87, 5D-91)

*Bjerknes, J., 1951 Extratropical cyclones. In: Compendium of Meteorology, Boston, pp. 577-598

*Bjerknes, V., J. Bjerknes, H. Solberg and T. Bergeron, 1933 : Physikalische Hydronamik. Berlin, J. Springer, 797 p. (4G-2)

Blair, C.F., Jr., 1951 : Flying the jet stream. Skyways, N.Y., 10 (9), 12-13 (4.4-175, 4G-62)

Bleeker, W., 1949 The relation between fronts and jetstream. BAMS 30, 190­ 191 (2.5-84) BIBLIOGRAPHY 69

Bleeker, W., 1950 The structure of weather systems. cPru~s, pp. 66-80 (2.3­ 67, 4G-63)

Bolin, B., 1950 On the influence of the earth's orography on the general character of the westerlies. Tel. 2, 184-195 (2.2-60)

*Bond, H.G., 1953 Easterly jet streams over Darwin. Wea. 8, 252-253 (5.1­ 135)

Boogaard, H.M. v.d., 1954 : Jet stream between Pretoria and Maun. So. Africa Wea. Bur. News Ltr., No. 63:8 (6.4-144)

Boville, B.W., W.S. Creswick and J.J. Gillis, 1955 :A frontal jet stream cross section. Tel. 7, 314-321 (7.10-153)

Bracelin, P., 1952 Notes on jet streams and turbulence at high levels. Great Brit. Admiralty. Naval Wea. Svc •• Circ., No. 15/ 52; M~S 161/52 (3K-190, 3K-211, 5D-203)

*Bradbury, D., and E. Palmen, 1953 : On the existence of a polar front at the 500 mb level. BAMS 34, 56-62 (5.1-145)

Briggs, J., 1952: Turbulence associated with a jet stream. MM 81, 119-120 (3K-191)

Brooks, C.E.P., C.S. Durst and N. Carruthers, 1946 : Upper winds over the world. Part I. The frequency distribution of winds at a point in the free air. QJ~S 72, 51-54

*Brooks, C.E.P., C.S. Durst, N. Carruthers, D. Dewar and J.S. Sawyer, 1950 : Upper winds over the world. GM 10, No. 85, 149 p. (10­ 117)

*Brundidge, K.C., 1956 : Analysis of selected project jet stream flight data. Texas A. and M. ColI., Dept. of Ocean~ Sci. Rep. No. 10 (Contr. AF 19 (604) - 559)(62 p.)(8.7-174)

Brunt, D., 1930 The present position of theories of the orIgIn of cy­ clonic depressions. QJ~S 56, 345-350 (Reprinted in : Some problems of modern meteorology. Roy. Meteor. Soc., London, 1934)

Buell, C.E., 1957 An approximate relationship between the variability of wind and the variability of pressure or height in the atmosphere. Bk~S 38, 47-51

Bundgaard, R.C., 1954 : Observations on billow clouds and deforming exhaust trails from aircraft. PTAC pp. 182-187 70 BIBLIOGRAPHY

Campbell Orde, A.C., 1952 : Some practical experience with civil jet trans­ port operation and associated meteorological problems. Aero. Eng. Rev., March 1952, 47-54

*Chambers, E., 1955 Clear air turbulence and civil jet operations. JRAS 59, 613-628 (7.7-61)

*Chaudhuri, A.M., 1950 : On the vertical distribution of wind and temperature over Indo-Pakistan along the meridian 76°E in winter. Tel. 2, 56-62 (3-87, 6-38, 4G-34)

Clapp, P.F., and J.S. Winston, 1951 :A case study of confluence as related to the jet stream. JM 8, 231-243 (3.5-224, 4G-63)

Clarkson, L.S., 1956 : Analysis of winds at 4C,OOO ft and 50,000 ft over Singapore. MM 85, 1-9

Clarkson, L.S., 1956 : Variation with time of winds at 40,000 ft and 50,000ft over Singapore. MM 85, 99-101

*Clem, Le R.H., 1954 : Clear-air turbulence at high levels. PTMe, pp. 193-198

Clem, Le R.H., De V. Colson and L.P. Harrison, 1954 : Corrections of upper­ level wind computations for effect of earth's curvature. Bk~S 35, 357-362

Clem, Le R.H., 1955 : Clear-air turbulence near the jet-stream maxima. BAMS 36, 53-60 (7.4-197)

*Clodman, J., 1957 Anisotropic high-level turbulence. QJm~s 83, 116-120

Co16n, J.A., 1951 On the wind structure above the tropopause over Puerto Rico. BAMS 32, 52-53 (2.11-118)

*Colson, D., 1954 Meteorological problems in forecasting mountain waves. BAMS 35, 363-371

*Coudron, J., 1952 Le jet et les courbes de variation de la vitesse moyenne du vent avec l'altitude. Jour. Scien. de la Meteor., 4, 143-148 (5D-247)

Coyle, J.R., 1950 The nature of sub-stratospheric conditions on the Buenos Aires-London air route. Panair do Brasil, Met. Serv., Brazilian Wea. Study, 10 p. (3C-32, 4G-35)

*Cressman, G.P., 1948 : On the forecasting of long waves in the upper wester­ lies. JM 5, 44-57 (4G-9)

*Cressman, G.P., 1950 : Variations in the structure of the upper westerlies. JM 7, 39-47 (5-4C, 4G-36) BIBLIOGRAPHY 71

*Crocker, A.M., W.L. Godson and C.M. Penner, 1947 Frontal contour charts. JM 4, 95-99

Crocker, A.M., 1949 : Synoptic applications of the frontal contour chart : the motion of selected lows, 5-7 November 1946. QJ~~S 75, 57-70

Crocker, A.M., 1952 : Jet stream in eastern North America on the afternoon of May 20, 1952. Canada. Met. Div•• Cir. 2153, Tec. 119 (4G-91)

Crossley, A.F., 1949 Equivalent head winds on air routes. JIN 2, 195-209

*Cunningham, N.W;, 1956 a : A study of thermal wind in the vicinity of a jet stream. Texas A. and M. ColI., Dept. Ocean., Sci. Rep. No. 8 (Contr. AF 19 (604)-559) (8.6-199)

*Cunningham, N.W., 1956 b : The frequency distribution of high velocity wind currents over Texas. Texas A. and M. College. Dept. Ocean•• Sci. Rep. No.9 {Contr. AF 19 (604)-559)(8.6­ 265)

Current Science, 1953 : "Jet Stream" under study. Curro Sci., Calcutta, 22, 135 (6.2-134)

Dahler, H., 1957 Zur Entstehung des Jetstreams und einige Folgerungen. Met. Runds. 10, 93-100

Dalziel, K., 1955: Rawin measurements at Heard Island. AMM No. 10, 47-56

Davies, D.M., 1950 : Atmospheric winds. JRAS 54, 602-605 (4G-37, 2.1-122)

*Davies, D.A., and Sansom, H.W., 1952 : Easterly jets over East Africa. Wea. ~ 343-344 (4.4-176, 4G-92)

Davis, N.E., 1951 The mean position of the jet stream. MRP 615 (4G-64)

*Davis, N.E., 1954 A successful transatlantic crossing in a jet stream. N~ 83, 268-271 (6.2-128)

Defant, A., 1949 Neuere Ansichten ueber die allgemeine Zirkulation der Atmosphaere in mittleren Breiten. m~GB Ser. A., 1:273­ 294 (4-54, 4G-19, 5D-148)

Defant, F., 1951 Die Aenderungen des meridionalen Windprofils durch Kon­ densationswaerme und Turbulenzvorgaenge. AMGB 4, 156-175 (3.3-106, 4B-253, 4G-65) 72 BIBLIOGRAPrrl

Defant, F., 1953 On the mechanism of index changes. Univ. Chicago. Dept. Meteor., Contr. N6 ori-20, T.O. II, Proj. NR 082 003, Tech Rep. May 1953 (5D-248, 7A-193)

Defant, F., 1956 Ueber die Struktur hochtroposphaerischer Duesenstroeme insbesondere des subtropischen Strahlstroms ueber Nord­ amerika. BDW No.4 (22), 126-133 (8.7-152)

*Defant, F., and H. Taba, 1957 : The threefold structure of the atmosphere and the characteristics of the tropopause. Tel. 9, 259-274

de Pasquale, 0., 1955 : Idee e applicazioni precorritrici di oltre 30 anni addietro sulle "correnti a getto". Riv. di Meteor. Aero. 15, 32-34 (8.1-198)

*Dickson, R.R., 1955 :A case study of the jet stream. BA~S 36, 195-203 (7.4­ 144)

Dickson, R.R., _1955 : Aids to jet stream forecasting. U.S. Office of Naval Operations, NAVAER, 50-1P-533. 53 p. (8C-67)

Dines, W.H., 1911 The vertical temperature distribution in the atmosphere over England, and some remarks on the general and local circulation. Phil. Trans. Roy. Soc. London, Ser. A., 211, 277-300

*Dobson, G.M.B., 1920 : Winds and temperature gradients in the stratosphere. QJRMS 46, 54-64

*Douglas, C.K.M., 1922 : Observation of upper cloud drift as an aid to re­ search and to weather forecasting. QJRMS 48, 342-356

Douglas, C.K.M., 1925 : On the relation between the source of the air and the upper air temperature up to base of the stratosphere. QJRMS 51, 229-238 (5D-50)

Due Rojo, A., 1954 El "Jet stream" 0 rio aereo estratosf~rico. Revista de Geofisica, Madrid, No. 49, 1954 (6.10-136)

Dunning, H.H., and N.E. La Seur, 1955 : An evaluation of some condensation trail observations. BAMS 36, 73-79 (6.9-248)

Dursi Moreau, E.V., 1954 : Corriente de "chorro". Rev. Nac. de Aeronaut. Buenos Aires, 14, 54-55 (6.2-129)

*Durst, C.S., and N.E. Davis, 1949 : Jet streams and their importance to air navigation. JIN 2, 210-218 (4G-20)

Durst, C.S., 1952 High level winds and temperatures for jet aircraft operation. QJru~s 78, 442-448 (4E-229). Discussion follows BIBLIOGRAPHY 73

Durst, C.S., 1952 The relation between wind flow over· British Isles and the Mediterranean. MRP 776, 2 p. (4E-230)

Durst, C.S., 1954 a : The accuracy of route wind forecasts for aviation. JIN 7, No. 1

Durst, C.S., 1954 b : Variation of wind with time and distance. GM 12, No. 93

Durward, J., 1921: Diurnal variation in wind velocity and direction at dif­ ferent heights. GBPN 15, 12 p.

Durward, J., 1925 The investigation of the winds in the upper air from in­ formation regarding the place of fall of pilot balloons and the distribution of pressure. GBPN 42, 13 p. (4G-l)

Durward, J ., 1936 Upper winds at Wadi Ha lfa (Sudan). GBPN 72, 11 p.

Durward, J., 1937 : Upper winds measured at MIY Imperia, Mirabella Bay, Crete. GBPN 79, 13 p.

Durward, J" 1938 : Upper winds at Nicosia (Cyprus). GBPN 87, 12 p. Durward, J., and D.C.E. Jones, 1955 : Weather phenomena at high levels. Aer. 88, 18-21 (6.9-151)

*Dwyer, W.A., 1953 Meteorology and the operation of high altitude aircraft. A~~ No.3, 22-37 (6.11-69)

Dwyer, W.N., 1955 Cloud forms associated with "jet stream". AMM No.8 55-56 (7.7-200)

Dykes, C., 1952 Some operating problems of future transport aircraft. JRAS 56, 189-200 (3K-210)

*Eady, E.T., and J.S. Sawyer, 1951 : Reviews of modern meteorology - Dynamics of flow patterns in extra-tropical regions. QJru~s 77, 531-551 (3.4-114, 4G-66)

Ekhart, E., 1940 Zur Kenntnis der Windverhaeltnisse in der oberen Stratos phaere. Berlin, Reichsamt fuer Wetterdienst, 50 p. (5D­ 108)

Ellison, T.H., and C.D. Walshaw, 1955 : The evaluation of some regression co­ efficients for estimating the 150 mb wind at Liverpool. QJRMS 81, 480-483

*Emery, P.F., 1956 Strong winds at high levels in the equatorial zone of the Far East. MM 85, 275-277 (8.2-128) 74 BIBLIOGRAPHY

Endlich, R.M., 1953 :A study of vertical velocities in the vicinity of jet streams. JM 10, 407-415 (5.6-117, 5H-90). See also Fleagle (letter) and Endlich (reply), JM 11, 513-514 (6.5-116)

*Endlich, R.M., P. Harney, G.C. McLean, and others, 1954 : Project jet stream. The observation and analysis of the detailed structure of the atmosphere near the tropopause. Bk~S 35, 143-153 (6.5-121)

*Endlich, R.M., S.B. Solot and H.A. Thur, 1955 : The mean vertical structure of the jet stream. Tel. 7, 308-313 (7.9-144)

Esso Air World, New York, 1951 : Clear air turbulence. Vol. 3, 128-130 (3K­ 168, 5D-180)

*Evans, Gwynne J., 1953 : Selective annotated bibliography on high level winds (500-100 mb). MAB 4, 613-655 (6B-150)

*Evans, G.J., and M.P. Kramer, 1953 a : Selective annotated bibliography on stratospheric and ionospheric winds (above 100 mb). MAB 4, 733-754 (6B-150)

*Evans, G.J., and M.P. Kramer, 1953 b : Annotated bibliography on the jet stream. MAB 4, 822-845 (6B-150)

Ewing, A., 1954 Jet stream steers the weather. Sci. News Ltr., 66, 362­ 364 (7.1-199)

Farkas, E., 1954 Upper winds over Canton Island and Tarawa. NZTN No. 115, Wellington, 5 p.

Farkas, E., 1955: Upper winds over Invercargill. NZTN No. 121, 6 p.

*Faust, H., 1953: Die Nullschicht, der Sitz des troposphaerischen Wind­ maximums. Met. Rundschau, 6, 6-15 (4E-253)

Faust, H., 1954 Die Strahlstroeme als Erscheinungen der Nullschicht. Met. Rund., 7, 161-166 (6.2-130)

Faust, H., 1955 Uebergradientische Winde in der Nullschicht und das Pro­ blem der Strahlstroeme. AMGB 8, 45-71 (6.8-10)

*Ference, M., 1951 Instrumentation and techniques for meteorological measurements. Compendium of Meteorology, Boston, pp.1207­ 1222

Fleagle, R.G., 1957 : On the dynamics of the general circulation. QJRMS 83, 1-20 BI BL IOGRAPHY 75

*Fletcher, R.D., 1953 : The association of wind speed with height of upper-air constant-pressure surface. BAMS 34, 155-159 (4G-131)

Flohn, H., 1950 a Die planetarische Zirkulation der Atmosphaere bis 30 km Hoehe. BDW No. 12, 156-161 (10-68)

*Flohn, H., 1950 b Grundzuege der allgemeinen atmosphaerischen Zirkulation auf der Suedhalbkugel. AN1GB 2, 17-64 (6-39, 4G-38)

Flohn, H., 1951: Die Zirkulation der Atmosphaere in den Polargebieten. Polarforschung, 3, 58-64 (3.3-108)

Flohn, H., 1951/52 Behrmann's "Prinzip der Selbstverstaerkung" in der Me­ teorologie und die Maeanderbildung in Atmosphaere und Ozean. Erde, Berlin, (3/4), 211-219 (3.10-109, 4G-93)

Flohn, H., 1952 Probleme der grossraeumigen Synoptik. BDW No. 35, 12-23 (3.10-72) Flohn, H., 1954 Investigations on the general atmospheric circulation, especially in lower latitudes. lAM pp. 431-442

*Foster, R.L., and E.F. Robinson, 1953 : The strong jet over the South-western Plains States, November 24-25, 1953. MNR 81, 374-378 (5.11-88)

Fotheringham, R.R., 1953 : High altitude winds at O.W.S. "Polar Front". MRP 812, 2 p.

Freeman, J.C., Jr.; J.T. Hurt; A. Kasahara, 1956 : Barotropic models of the jet stream. Texas A. &M. ColI. De t. Ocean. and Meteor., Sci Rep. No. 12 Contr. AF 19 (604)-559)(98 pp.) (8.6-2)

*French, J.E. and K.R. Johannessen, 1954 : Forecasting high clouds from high­ level constant-pressure charts. PTMC, 160-171 (6.3-75)

*Frost, B.C., 1953: Flying in jet stream winds. Shell Av. News, No. 186, 4-8 (5.9-203)

*Frost, B.C., 1954 More about the jet stream. Shell Av. News, No. 195, 14­ 18 (6.6-253, 7.7-62)

Frost, B.C., 1955 Novos fatos s8bre 0 jet stream. Aviacao, Rio de Janeiro, 17, 288-299

*Frost, R., 1952 The upper air circulation in low latitudes and its rela­ tion to certain climatological discontinuities. MRP 706 (3.7-87, 4G-94) 76 BIBLIOGRAPHY

Fuglister, F .C., 1951 : Multiple currents in the Gulf-stream system. Tel. 3, 230-233

Fultz, D., 1949 A preliminary report on experiments with thermally pro­ duced lateral mixing in a rotating hemisph~rical shell of liquid. JM 6, 17-33 (3-43)

Fultz, D., 1951 Experimental analogies to atmospheric motions. Compen­ dium of Meteorology, Boston, 1951. pp. 1235-1248

*Gabites, J.F., 1952 : Mean westerly wind flow between the 700 and 100 milli­ bar levels over the New Zealand region. NZTN No. 90 (4G-95)

Gabites, J.F. and E.M. Porter, 1952 : Equivalent head winds on air routes leading to New Zealand. NZTN No. 86, 4 p. (4E-234)

Gabites, J.F. and E.M. Porter, 1952 : Equivalent head winds at 30,000 ft on South Pacific air routes during 1951. NZTN No. 83, 4 p. (4E-234)

Gabites, J.F., 1953 : Mean westerly wind flow in the upper levels over the New Zealand region. New Zeal. Jour. Sci. and Technol., Sec. B. 34, 384-390 (4G-123)

Gales, D.M., 1955 Airways weather San Francisco-Cheyenne. Trans World Air­ lines, Inc., Jan. 15, 1955. 23 p. (7.3-63)

Garriock, A., 1955 A case of clear air turbulence at medium altitudes. A~n No.9, 44-54

Gazzola, A., 1954 Le jet stream dans une situation de bloquage. lAM, pp. 44-49

*Gazzola, A., 1955 La corrente a getto durante une situazione di blocco. Riv. di Meteor. Aero., Rome, 15, 25-31 (8.1-193)

General Electric Review, 1953 : "The jet was chasing its tail". G.E. Rev., 56, 42-47 (4G-132)

Georgi, J., 1950 Hochstuerme ueber der Daenemarkstrasse. Deutsche Hydrogr. Zeits., 3, 136-143 (4G-39)

Georgii, W., 1953 1. Problemas de la corriente ondulatoria y de chorro en la Argentina. Rev. Nac. de Aeronaut., Buenos Aires, 13, 33-37; 2. La corriente atmosferica de chorro. Ibid., 13, 42-45 (5.7-128, 5H-126)

*Gibbs, W.J., 1952 Notes on the mean jet stream over Australia. JM 9, 279­ 284 (4.2-107, 4D-263, 4G-96) BIBLIOGRAPHY 77

*Gibbs, W.J., 1953 A comparison of hemispheric circulations with particular reference to the western Pacific. QJFlliIS 79, 121-136 (4D-270, 4G-124)

*Gibbs, W.J., 1955 200 mb divergence associated with rapid and intense cyclogenesis. ANV~ No. 11, 17-35

Gilchrist, A., 1953 : Upper winds in the tropics and subtropics. MRP 795, 12 p. (5D-223)

*Gilchrist, A., 1955 : Winds between 300 and 100 mb in the tropics and sub­ tropics. GBMR No. 16, 28 p.

Girs, A.A., 1955 K voprosu ob izuchenii obshchel tsirkuliatsii atmosfery. (Investigation of the general circulation of the atmo­ sphere.) Akademiia Nauk SSSR, Izvestiia, Ser. Geo9., No. 4, 16-28 (7.10-149)

Godson, W.L., 1955 Arctic jet streams and high-level turbulence. In : Sci. Pap. No.1, Arctic Met. Group, McGill Univ. (Contr. AF 19 (604)-1141) (8.4-179) Gold, E., 1953 The variation of wind near the tropopause. MM 82, 194­ 198 (4.11-192, 5D-224)

*Goldie, A.H.R., 1937 Kinematical features of depressions. QA No. 72

*Goldie, A.H.R., 1939 Depressions as vortices. QA No. 79

Goldie, A.H.R., 1947 The upper atmosphere. Estimated distribution of tem­ perature, pressure and wind up to the 45 km level. MRP 360,6 p.

Goody, R.M., 1954 The physics of the stratosphere. Cambridge monog. on Phys., Cambridge Univ. Press, 187 p. (5D-231)

Grant, A., 1952 A re-examination of the zonal-wind profile under condi­ tions of constant vorticity. JM 9, 439-441 (4.7-73)

Gray, G.J., Jr., 1951 : Jet streams and aircraft operations. ~Ni. 4, 99-101; III (3.4-118, 4G-67)

Gray, R. and N. Carruthers, 1951 Upper air over the Falkland Islands. MAl 80, 125-130 (2.11-181)

Great Brit. Met. Off., 1950 : Equivalent headwinds on some of the principal air routes of the world. GBMR No.7, 19 p. (11-116, 4E­ 192) 78 BIBLIOGRAPHY

Great Brit. Met. Off., 1951 : Upper air climatology of the Southern Hemi­ sphere. Discussion. MM 80, 52-56 (2.8-159)

Great Brit. Met. Off., 1951 : Measurement of upper winds. Discussion. MM 80, 83-86

Great Brit. Met. Off., 1952 : Winds in the stratosphere over Great Britain. Discussion. WA 81, 14-18

Great Britain Met. Off., 1952 : Forecasting winds at 30,000 - 40,000 feet and above. Discussion. MM 81, 79-85 (3.9-69)

*Great Britain Met. Off., 1955 : Forecasting for long distance flights. ~~ 84, 79-89

Great Brit. Nav. Wea. Serv., 1952 : Notes on jet streams and turbulence at high levels. Gt. Brit. Nav. Wea. Serv'l Circ. No. 15/52, 7 p.

Grover, J.H.H., 1955 Operational aspects of jet streams. Aeronautics, London, 32, 102-105 (7.2-134)

*Gustafson, A.F., 1949 : Final report on the upper winds project. Dept. Me­ teor. Univ. Calif. Los Angeles

*Gustafson, A.F., 1954 : The error in rawin computations due to neglecting the earth's curvature. BAMS 35, 295-300

*Gutenberg, B., 1949 New data on the lower stratosphere. BAMS 30, 62-64

Harding, E.T., 1954 Jet stream research in the Navy. Wwi. 7, 3-6 (6.2-131)

Harding, J., 1955: The profile of jet streams in the Middle East. MRP 932, 11 p. (7.5-121)

Harley, D.G., 1954 Equivalent tail winds pn the Shannon to Gander route. JIN,Jan. 1954, see also MRP 749, 1952

*Harrison, H.T., Jr., 1950 : Some characteristics of the upper level LOW and the jet stream. United Airlines, Inc. ~~teor. Circ., No. 34 (3K-151, 4G-40)

*Harrison, H.T., 1951 : Some meteorological problems indicated for jet trans­ port operation at 40,000 feet. Aero. Eng, Rev., Apr. 1951, 52-61 (3.1-17, 5D-187)

Haurwitz, B., 1954 Zonal wind field in the upper atmosphere. New York Univ., Res. Div., Contract AF 19 (122)-49, Scien. Rep. No.7, Feb.~54 (6.9-223) BIBLIOGRAPHY 79

Hay, R.F.M., 1952 Wind at high levels over Hong Kong. MRP 778, 6 p. (4E­ 239)

*Hay, R.F.M., 1953 High level strong easterlies over Singapore and Hong Kong. Wea. 8, 206-208 (See also MRP 770, 1952)

Heastie, H., 1955 Average height of the standard isobaric surfaces over the area from the North Pole to 55oN in January. MRP 918 (6.ll-272)

Heines, J.M., 1956 Jet stream navigation. Shell Avia o News, London, No. 212, 14-18 (8.2-129)

Herbst, W., R. Neuwirth and K. Philipp, 1954 : Betrachtungen ueber die Eignung radioaktiver atomtechnischer Aeroso1e a1s Markierungs­ mittel bei Arbeiten auf dem Gebiete der Meteorologischen Stroemungsforschung. ~atu~iss., 41, 156-160 (5.8-276, 7E-68)

*Hess, S.L., 1948 Some new meridional cross-sections through the atmo­ sphere. JM 5, 293-300 (4G-10)

*Hesselberg, Th., 1913 : Die Luftbewegung im Cirrusniveau. Veroeff. Geophys. Inst. Univ. Leipzig, Serie 2, Band 1, 17-73

Hi1debrandsson, H.H., 1898 : Etudes internationa1es des nuages 1896-1897. Observations et mesures de 1a Suede. Upsala, 182 p. (4E-254)

Hille, A., 1954 Trans. (Jet streams and frontal zones in the upper air). Tdoejaras, 58, 90-95 (6.2-132)

Hislop, G.S., 1949 Clear air turbulence incident encountered by D-H "Comet" aircraft 14 November, 1949. Brit. Eur. Airways Corp., R.S.D. Note, No. 41 (3K-133, 4G-21)

Hislop, G.S., 1950 Gusts from a clear sky. ~~craft, Melbourne, 29; 18-19, 40-41 (4E-193)

Hislop, G.S., and D.M. Davies, 1950 : An investigation of high altitude clear­ air turbulence over Europe using Mosquito aircraft. Gt. Brit. Aeronaut. Res. Council, Rep. and memoranda, No. 2737 (6.2-199)

*Hislop, GoS., 1951 Clear air turbulence over Europe. JRAS 55, 185-225 (3K­ 172, 5D-188)

Hofmeyer, W.L., 1950 : Remarks on the theory of the jet stream. JM 7, 245 (4G-41) 80 BIBLIOGRAPHY

*Hofmeyer, W.L., 1952 :A statistical analysis of radar winds over Pretoria in winter. Notos, 1, No.4, 186-192

*Hofmeyer, W.L., 1953 :A statistical analysis of radar winds over Pretoria in summer. Notos, 2, No.3, 144-148

Hollman, G., 1954 Zur Frage des Nullschichteffekts und der Strahlstroeme. Met. Runds., 7, 166-170 (6.2-133)

Hovmoeller, E., 1948 : North-south cross section showing distributions of temperature, relative hllinidity and wind in a well-marked zonal current over western Europe. JM 5, 67-69 (4G-ll)

Hovmoeller, E., 1950 : Zonal and meridional air currents in the stratosphere

over Europe. GPA 17, 112-120 (2 0 5-66, 4E-194)

Hoyle, H.D., 1955 The subtropical jet-stream of the North Pacific in Janu­

ary and April 1952 0 MRP 924, June 28, 1955. 8 po (7.5-122)

Hsieh, Y.-P., 1949 An investigation of a selected cold vortex over North America. JM 6, 401-410 (3-46)

Hsieh, Y.-P., 1950 a : On the formation of shear lines in the upper atmosphere. JM 7, 382-387 (2.4-74)

*Hsieh, Y.-P., 1950 b : The mean wind and temperature distribution through a flat upper ridge in winter. Tel. 2, 130-133 (11-71, 4G-42)

Hubert, W.E., 1953 A case study of variations in structure and circulation about westerly jet streams over Europe. Tel. 4, 359-372 (5.7-86)

*Hubert, W.E. and Y. Dagel, 1955 : Upper mean flow over the North Atlantic during January 1952. Tel. 7, 111-117 (6.10-193)

Hughes, G.D. and R.I. Foster, 1954 : The tropopause during a major change in circulation over the Western United States, November 25 to 28, 1954. M~R 82, 343-353 (6.11-172)

*Hurst, G.W., 1952 The profile of a jet stream observed 18 January 1952. QJRMS 78, 613-615 (3.10-196, 4G-98)

*Hurst, G.W., 1953 The profile of a jet stream observed 1 September 1952. QJRMS 79, 407-411

*Hutchings, J.W., 1950 :A meridional atmospheric cross section for an oceanic region. JM 7, 94-100 (7-40, 4G-43, 41-252, 5D-167)

Hutchings, J.W., 1952 a : A note on the distribution of free air wind vectors about their mean. QJRMS 78, 105-106 BIBLIOGRAPHY 81

*Hutchings, J.W., 1952 b : The winter jet-stream in the Southern Hemisphere.

Wea. 7, 73-77 (3 0 5-143, 4G-99) (See also Wea. 7, 258)

*Hyde, E.A., 1954 Clear air turbulence and its allied phenomena. ~~. ~, No. 192, 14-15

Iselin, C.O., 1950 Some common characteristics of the Gulf-stream and the atmospheric jet stream. N.Y. Acad. Sci., Transactions, 2nd ser. 13, 84-86 (3.4-115, 4G-44)

Ishimaru, Y., 1952 Fundamental vorticity equation and jet stream mechanism. Mechanism of the earth's atmosphere, 4th communication. Geophys. Mag., 24, 41-80 (4G-IOO, 6.1-127)

Ishimaru, Y., 1954 On the zonal circulation and its perturbation. (Mecha­ nism of the earth's atmosphere, 5th communication. Geo­ phys. Mag., 25, 123-149 (5.9-127)

Isozaki, I., 1952 A mechanism of pressure disturbance. J. Met. Res., Toky~ 4, 97-105 (5.4-147)

Izawa, T., 1950 On the upper distur.bances in the westerlies whose mean circulation have longitudinal wind gradient (in Japanese). JMSJ 28, 224-232 (2.7-80)

*Jacobs, L.E., 1955 Navigational aspects of the jet stream. Navigation, 4, 242-249 (7.4-145)

James, D.G., 1953 An account of one of the methods employed in the investi­ gation of clear air turbulence. MRP 792, 7 p.

James, R.P., and G.C. Holzworth, 1954 : Some fluctuations in the jet stream and tropopause associated with cyclonic development and movement, February 18-21, 1954. MWR 82, 64-72 (6.6-173)

James, R.W., 1951 A February cross-section along the Greenwich meridian. MM 80, 341-346 (3.6-84, 4G-68)

James, R.W., 1952 On the vertical structure of pressure and wind-fields. A~GB 5, 17-35 (3.10-112)

Jenista, C.O., Jr., 1953 :A statistical study of precipitation distribution as related to various types of mean zonal motion. BANIS 34, 10-13 (4.11-220)

*Jenkins, C.F., 1952 Forecasting the mountain wave. AFSG No. 15 (5.1-211)

Jenkins, C.F., and J. Kuettner, 1953 : Flight aspects on the mountain wave. AFSG No. 25 82 BIBLIOGRAPHY

*Jenkinson, A.F., 1954 : Upper winds from nephoscope observations. MM 83, 174­ D5

*Jenkinson, A.F., 1955 : Average vector wind distribution of the upper air in temperate and tropical latitudes. MM 84, 140-147 (6.10­ 197)

Jenkinson, A.F., 1956 : The relation between standard deviation of contour height and standard vector deviation of wind. QJRMS 82, 198-208

Johnson, DoH., 1952 : Further notes on the wind field of middle latitudes. MRP 761 (4.6-151, 4G-I02)

Johnson, D.H., 1953 a The accuracy of 100 mb contour heights. MRP 800, 3 p.

*Johnson, D.H., 1953 b Jet stream of October 28, 1952. MM 82, 178-182 (4G­ 133)

Johnson, D.H., 1953 c : The jet stream. Parts I and II. Wea. 8, 270-274; 325-329 (5.4-163)

*Johnson, D.H., 1953 d : A further study of the upper westerlies; the struc­ ture of the wind field in the eastern North Atlantic and western Europe in January 1950. QJRMS 79, 402-407 (4.11-193)

Johnson, D.H., and S. Daniels, 1954 : Rainfall in relation to the jet streams. QJRMS 80, 212-217 (5.6-220, 5H-96)

du Jonchay, I., 1952 : L'importance des vents portants en altitude notamment dans Ilhemisphere sud. GPA 21, 52-57 (3.11-163)

Jones, D.C.E., 1953 : Investigation of high altitude clear air turbulence near jet streams: special flights by R.A.F. and R.A.E. aircraft. MRP 827, 4 p. (5.6-163)

Jones, D.C.E., 1953 : Weather systems associated with some occasions of severe turbulence in clear nir at high altitude : a further analysis. MRP 828 (5.6-163)

*Jones, D.C.E., 1954 : Further investigations of high-level clear-air turbu­ lence. MM 83, 166-173 (5.9-184)

*Jones, D.C.E., 1955 : Exceptionally severe clear-air turbulence and other phenomena on 14 April, 1954. MM 84, 107-111(6.7-223)

*Jones, F.E., 1949 Radar as an aid to the study of the atmosphere. JRAS 53, 437-448 BIBLIOGRAPHY 83

Jones, J.J., 1951 The physical causecl the jet stream in the Japanese area. U.S. Air Force 2143 D Air W~a. Wing Tech. Bull. 1 (7), 4-21 (3.6-85, 4G-77)

Kasahara, A., 1950 On the dynamical mechanism of the high tropospheric jet stream. Tokyo, Univ. Geophys. Inst., Geophys. ~, 3(31), 10 p.; also Collected Meteor. ~apers, 2(2) (2.10­ 72, 4G-45)

Kasahara, A., 1956 Three dimensional structure of small-scale atmospheric perturbations aloft. Texas A. and M. ColI. Dept. of Ocean., Sci. Rep. No.7 (Contr. 'AF (604)-559) (39~) (8.6-201)

Kaufman, P., 1950 Bemerkungen zum jet-stream in Atlantik-Wetterdienst. BDW No. 12, 200-201 (10-61)

*Kelly, R.C., and H.B. Caster, 1954 : Simulated jet transport operation. Soc. Automotive Engrs., N.Y., S.A.E. Preprint, No. 298 (6.7­ 92)

Khrgian, A.K.H., 1953 : Fizika a~osfery. Mosc~~. 456 p. (5D-243, 5.7-7)

Kimpara, A., 1953: A~~ospherics due to fronts in the upper atmosphere. Nagoya Univ., Res. Inst. of Atmospherics, Proc., 1, 45­ 49 (4K-263)

Klein, W.H., 1951 A hemispheric study of daily pressure variability at sea level and aloft. JM 8, 332-346

Klein, W.H., 1954 The weather and circulation of April 1954 :A month with a confluent jet stream. AWIR 82, 104-109 (6.5-122) *Kleinschmidt, E., Jr., 1941 : Stabilitatstheorie des geastrophischen Wind­ feldes. Ann. Hydrogr., Berlin, 69, 305-325

Kleinschmidt, E., Jr., 1955 : Die Entstehung einer ~6henzyklone tiber Nord­ amerika. Tel. 7, 96-110 (7.11-178)

Klieforth, H.M., 1955 : Mountain wave - jet stream project. Dept. Meteor. UCLA, Final Report, Contr. AF 19(604)-1308 (8.3-235) Knighting, E., 1954 Upper winds over the world. QJRMS 80, 239-240

Kobayashi, Y., 1951 On the zonal component of upper wind at Tateno. J. Aero. obs., Taten~, Japan, 5, 37-41 (4E-268)

*Kochanski, A., 1955 : Cross sections of the mean zonal flow and temperature along 80oW. JM 12, 95-106 (6.8-202) 84 BIBLIOGRAPHY

Koo, C.-C., 1955 Der dynamische Einfluss des Hochlandes von Tibet auf die ostasiatische Zirkulation. Acta A ronomica, Budapest, 5, 273-284. Also (in Hungarian Idojaras, 59, 204-211

*Koteswaram, P., 1953 : An analysis of the high tropospheric wind circulation over India in winter. IJMG 4, 13-21 (4G-125)

Koteswaram, P., C.R.V. Raman and S. Parthasarathy, 1953 : The mean jet stream over India and Burma in winter. IJMG 4, 111-122 (4G-134, 5B-309)

Koteswaram, P., and S. Parthasarathy, 1954 : The mean jet stream over India in the pre-monsoon and post-monsoon seasons and vertical motions associated with subtropical jet streams. IJMG 5, 138-156 (8.1-201)

*Koteswaram, P., 1956 : Easterly jet stream in the tropics. Vniv. Chicago. Dept. Meteor., Rep. on Res., Proj. NR 082-120 (Contr. N 6 ori -02036) (8.6-202)

Koteswaram, P., 1957 : Mean zonal wind circulation over India. IJMG 8, 346­ 347

*Kramer, M.P., and M. Rigby, 1952 : Selective annotated bibliography on atmo­ spheric turbulence and "bumpiness" in flight. MAE 3 (11), 1185-1219 (3K-, 4G-l03)

*Krishna Rao, P.R., 1952 : Probable regions of "jet" streams in the upper air over India. Curro Sci., Bangalore, 21, 63-64 (3.10-197, 4G-104)

Kuettner, J., 1952 On the possibility of soaring on travelling waves in the jet stream. ~ing, 16, 9-14 (3K-197, 4G-l05)

Kuettner, J., 1952 Note on high level turbulence encountered by a glider. AFSG No. 29, 3 p. (6.2-204)

Kuettner, J., 1955 The exploration of the jet stream by sailplanes. Soaring, 19, 11-13,. 16-17 (7.7-143) Kuo, H.-L., 1950 The motion of atmospheric vortices and the general cir­ culation. JM 7, 247-258 (2.2-66)

*Lake, H., 1956 A meteorological analysis of clear air turbulence. GRP 47, 63 p. (See correspondence, Arakawa and Lake: Clear­ air turbulence associated with negative vertical wind shear. JM 14, 188-190)

Lamb, H.H., 1952 The jet stream in the Southern Hemisphere. Wea. 7, 258 (4G-106) BIBLIOGRAPHY 85

Lamb, H.H., 1957 Some interesting properties of the "Nullschicht" or maximum wind layer. MNI 86, 142-145

Lamb, H.H., J. Fleming, H.D. Hoyle and J. Robinson, 1957 : Jet streams over North Africa and the central Mediterranean in January and February 1954. MIA 86, 97-111 (8.8-203)

*Landers, H., 1955 Analysis of some "Project Jet Stream" data. BAMS 36, 371-378 (7.9-145)

Lee, R., 1955 Synoptic evidence for a direct circulation about a jet stream. QJru~s 81, 462-468 (6.11-201)

*Lee, R., and Godson, W.L., 1957 : The arctic stratospheric jet stream during the winter of 1955-56. Journa; of Meteorology, 14, 126­ 135

Lettau, H., 1956 Theoretical notes on the dynamics of the equatorial at­ mosphere. Beit. Z. Phy~. der Atmos., 29, 107-122

*Loewe, F., and V. Radok, 1950 :A meridional aero1ogica1 cross-section in the South-West Pacific. JM 7, 58-65; 305-306 (revision) (5-101, 2.2-151, 4G-46 , 5D-172)

Magata, M., 1950: On the structure of the jet stream. PMG 175-187

Ma1et, L.M., 1954: Diverses experiences de comparaison de radiosondes. World Met. Org., Ol~, No. 35.TP.11, Tech. Note, No.5, 1954 (7.2-93)

*Ma1kus, J.S., and C. Ronne, 1954 : On the structure of some cwnu10nimbus clouds which penetrated the high tropical troposphere. Tel. 6, 351-366

*Matswnoto, S., H. Itoo and A. Arakawa, 1953 : On the monthly mean distribu­ tion of temperature, wind and relative humidity of the atmosphere over Japan from March 1951 to February 1952. JMSJ 31, 248-258 (5.10-42)

McClellan, D.E., 1954 : Jet stream analysis. Can. Met. Div., Cir. -2425, TEC-179, Feb. 1, 1954 (6.2-72, 6.7-171)

McIntyre, D.P., 1951 : Some trends in modern meteorology. Phys. i~_~~, Toronto, pp. 13-17 (5.2-10)

*McIntyre, D.P., and R. Lee, 1953 : Jet streams in middle and high latitudes. PTye 172-181 (6.3-109)

*McIntyre, D.P., 1955 : On the baroc1ine structure of the westerlies. JM 12, 201-210 (6.9-155) 86 BIBLIOGPJWHY

McClean, G.S., and R.M. Rados, 1955 : Project jet stream observation of a small-scale high-level vortex. BAMS 36, 469-474 (7.11­ 181)

*McTaggart-Cowan, P.D., 1950 The jet stream. Roy. meteor. Soc. Canadian Br., 1, No. 1 (2.9-80, 4G-47)

*Means, L.L., 1954 A study of the mean southerly wind-maximum in low levels associated with a period of summer precipitation in the Middle West. BAMS 35, 166-170 (6.4-145)

Miles) M.F., 1952: Temperature and wind distribution in the lower strato­ sphere. MM 81, 212-215

*Mintz, Y., and G.A. Dean, 1952 : The observed mean field of motion of the atmosphere. GRP No. 17, 65 p.

~~intz, Y., 1954 The observed zonal circulation of the atmosphere. BAMS 35, 208-214

*Mironovitch, M.V., 1953 : Representation de la circulation atmospherique ge­ nerale pour une coupe aerologique meridienne a travers les deux hemispheres. Acad. des sci., Paris Comptes Ren­ dus, 236(4), 404-406 (4G-126, 5D-227, 5.1-136)

*Mohri, K., 1953 On the fields of wind and temperature over Japan and ad­ jacent waters during winter of 1950-1951. Tel. 5, 340­ 358 (5.9-131)

*Moir, R.W., 1950 A brief note on the upper winds at 30,000 ft over Nandi, Fiji. NZCN No. 59, 2 p.

*Mook, C.P., 1952 A meteorological analysis of reports of turbulence en­ countered by aircraft in clear air. Aer. Eng. Rev., N.Y., 11, 22-27 (3K-200)

Moore, J.G., 1956 Cross-sections of the mean zonal component of geostro­ phic wind. MM 85, 167-171.

Murakami, T., 1951 On the study of the change of the upper westerlies in the last stage of Baiu season (Rainy season in Japan). JMSJ 29, 162-175 (3.3-109, 4G-71) (in Japanese)

*Murakami, T., 1953 On the seasonal variation of upper flow patterns. Part I. From winter to spring. JMSJ 31, 173-193 (5.9-204)

*Murgatroyd, R.J., 1957 : Winds and temperatures between 20 km and 100 km - a review. QJru~s 83, 417-458 BIBLIOGRAPHY 87

Murray, R., 1951 Practical value of the contour chart as a method of re~ presenting upper winds. Summary of results. MRP 663, 5 p.

Murray, R., and S. Daniels, 1951 : Transverse flow at entrance and exit to jet streams. QJffi~S 79, 236~241 (3.11-116, 4G-72) (See also QJRMS 80, 112-113)

Murray, R., 1952 The jet streams over the British Isles during 14~18 June 1951. MRP 743 (4.5-133, 4G-135)

*Murray, R., and D.H. Johnson, 1952 : Structure of the upper westerlies; a study of the field in the eastern Atlantic and western Europe in September 1950. QJRMS 78, 186-199 (3.8-6, 4G~ 108)

Murray, R., 1953 The upper troposphere and lower stratosphere near jet streams : an examination of observations by the Meteoro­ logical Research Flight, Farnborough. MRP 813, 18 p. (5.3-143)

Murray, R., 1954 On the accuracy of contour charts in forecasting upper winds. GBPN No. 110, 11 p.

*Murray, R., 1956 Some features of jet streams as shown by aircraft ob­ servations. GM No. 97 (7.6-9)

*Namias, J., 1947 Physical nature of some fluctuations in the speed of the zonal circulation. JM 4, 125-133 (4G~7)

*Namias, J., and P.F. Clapp, 1949 : Confluence theory of the high-tropospheric jet stream. JM 6, 330-336 (2~78, 4G~22)

*Namias, J., 1950 The index cycle and its rale in the general circulation. JM 7, 130-139 (7-41)

Namias, J., 1951 Meteorology in navigation. Inst. Navig., Los Angeles, 7th Ann. Mtg., N.Y. City, 1951 (3.10~198, 4G-73)

*Namias, J., and P.F. Clapp, 1951 : Observational studies of general circula­ tion patterns. Compendium of Meteorol£gy, Amer. Meteor. Soc., 551-567

Namias, J., 1952 : The jet stream. Sci. Am •• 187, 26-31 (4.5-94, 4G-I09)

National Advisory Committee for Aeronautics, 1955 : Meteorological problems associated with commercial turbojet - aircraft opera~ tion. NACA Research Memorandum, ffi~54L29, Washington, June 21, 1955, 46 p. 88 BIBLIOGRAPHY

*Newton, C.W., N.A. Phillips, J.E. Carson and D.L. Bradbury, 1951 : Structure of shear lines near the tropopause in summer. Tel. 3, 153-171 (3.11-120, 4G-74)

*Newton, C.W., and J.E. Carson, 1953 : Structure of wind field and variations of vorticity in a summer situation. Tel. 5, 321-339 (6.1-212)

*Newton, C.W., 1954 Frontogenesis and frontolysis as a three-dimensional process. JM 11, 449-461 (6.5-139)

New York Times Mag., 1955 : The jet stream. N.Y. Times Mag., Sec. 6, p. 40, Jan. 2, 1955 (7.5-123)

Nojima, H., 1954 The jet streams over Honjo and Tateno in the winter season 1951-1952. J. Aero. Obs. Tateno, 5, 219-232; The easterlies in the lower stratosphere observed over Honjo and Tateno in January and February 1952. Ibid., 233-244 (8.4-184) -----

*Nyberg, A., 1945 Synoptic-aerological investigation of weather condi­ tions in Europe, 17-24 April 1939. Statens Meteor.­ Hydrog. Anstalt, Comm., Ser. of pap., No. 48, 122 p. (Stockholm)

*Nyberg, A., 1949 An aerological study of large-scale atmospheric disturb­ ances. Tel. 1 (1), 44-53 (4G-23)

Nyberg, A., 1950 I A study of vertical motion and formation of fronts and jet streams. CPRMS pp. 81-89 (2.5-85, 4G-49)

Nyberg, A., 1953 Note on "A further study on the relation between the jet stream and cyclone formation". Tel. 5, 316-317 (5.7-88); Riehl, H., reply, 317-318

*Ockenden, C.V., 1939 : High altitude pilot balloon ascents at Habbaniya, Iraq. QJRNIS 65, 551-553

Oliver, V.J., 1947 The forecasting significance of high level winds in sub­ Arctic regions. BAMS 28, 9-14 (4G-S)

*Ooi, S., S. Matsumoto and H. Itoo, 1951 :A study on westerly troughs near Japan (I). PMG 2, 219-233. Ooi, S., S. Matsumoto, H. Itoo and A. Arakawa, 1952 :.(11). PMG 3, 1-11; Matsumoto, S., H. Itoo and A. Arakawa, 1953 : •• (111). PMG 3, 229­ 245 (4.11-116)

Painter, H.E., 1952 : Vertical currents observed at Habbaniya, May 6, 1952. MM 81, 339-340 BIBLIOGRAPHy 89

Palmen, E., 1935 Registrierballonaufstiege in einer tiefen Zyklone. Finska Vetenskaps - Soc., Helsinki, Corom. Phys.-M~., 8(3), 1-32 (5D-79)

Palmen, E., 1948 a Discussion of problems concerning frontal analysis in the free atmosphere. Ibid., 8 (8), 47 p. (2.6-31)

*Palmen, E., 1948 b : On the distribution of temperature and wind in the upper westerlies. JM 5, 20-27 (5-42, 4G-12)

*Palmen, E., and K.M. Nagler, 1948 : An analysis of the wind and temperature distribution in the free aLmosphere over North America in case of approximately westerly flow. JM 5, 58-64 (4G-13, 5D-144)

*Palmen, E., and C.W. Newton, 1948 :A study of the mean wind and temperature distribution in the vicinity of the polar front in winter. JM 5, 220-226 (4G-14)

Palmen, E., 1949 On the origin and structure of high level cyclones south of the maximum westerlies. Tel. 1 (1), 22-31 (4G-24)

*Palmen, E., and K.M. Nagler, 1949 : The formation and structure of a large scale disturbance in the westerlies. JM 6, 227-242 (4G­ 25)

*Palmen, E., 1951 a The rale of atmospheric disturbances in the general cir­ culation. QJRMS 77, 337-354 (2.10-71, 4G-75)

*Palmen, E., and C.W. Newton, 1951 : On the three-dimensional motions in an outbreak of polar air. JM 8, 25-39

*Palmen, E., 1951 b The aerology of extratropical disturbances. In Compen­ dium of Meteorology, Boston., pp. 599-620 (3.5-8, 5D­ 239)

Palmen, E., 1954 Uber die atmospnarischen Strahlstrome. Berlin. Freie Univ. Inst. of Met. u. Geophys~t. Abh., 2, 35-50 (6.9-156)

Palmer, C.E., 1954 The general circulation between 200 mb and 10 mb over the equatorial Pacific. Wea. 9, 341-349 (6.3-110)

*Palmer, C.E., C.W. Wise, L.J. Stempson and G.H. Duncan, 1955 : The practical aspects of tropical meteorology. Univ. Calif. Los Angeles, Oahu Res. Cen., Spec. Rep. No.2 (AFCRC-TN-55­ 460); AWSM 105-48 (195 p.)

Pellisari, L., 1953 : Le "raffiche in aria limpida". Rivista di Meteor. Aero­ !l~tica, 13, 53-54 (5.8-164) 90 BIBLIOGRAPHY

Perry, I., 1954 Some aspects of Comet flight of interest to the navi­ gator. Navigation 4, 42-51

*Petterssen, 5., 1950 : Some aspects of the general circulation of the atmo­ sphere. cpm~s, pp. 120-155 (2.3-62)

Petterssen, 5., 1952 : On the propagation and growth of jet-stream waves. QJm~S 78, 337-353 (4.2-176, 4G-IIO)

*Petterssen, 5., 1956 : Weather analysis and forecasting. (2nd ed.) Vol. I, McGraw-Hill, New York, 428 p. (See pp. 112-121)

*Phillips, N.A., 1950 : The behaviour of jet streams over eastern North fu~erica during January and February 1948. Tel. 2, 116­ 124 (11-62, 4G-50)

Phillips, N.A., 1956 : The general circulation of the atmosphere A numeri- cal experiment. QJm~s 82, 123-164

Phillpot, H.R., and D.G. Reid, 1952 : Equivalent headwinds on Australian air routes. Comm. Australia Bur. Meteor., Bull. No. 41, Melbourne, 24 p.

Platzman, G.W., 1949 : The motion of barotropic disturbances in the upper

troposphere Q Tel. 1, No.3, 53-64

Porter, E.M., 1951 Some observations of a "jet stream" in the New Zealand region. NZCN 74 (4G-76)

*Porter, E.M., 1952 a Upper winds over Nandi and Auckland. NZTN 92, 8 p.

*Porter, E.M., 1952 b Upper winds over Invercargill. NZTN 94, 5 p. (See Farkas, 1955)

Porter, E.M., 1953 The westerly wind flow at 300 mb across Australia and New Zealand. NZTN 98 (5.4-165)

*Pothecary, I.J.W., 1953 : Clear-air turbulence at 20,000 feet in a frontal zone. M~ 82, 175-178

Prandtl, L., 1949 Wettervorgange in der oberen Tropospnare. Akad. Wiss. in Gottingen, Math.-phys. Klasse, Math.-phys.-chem. Ab­ teil., Nachrichten, No.2: 13-18 (4.3-119, 4G-26)

Prandtl, L., 1950 Dynamische Erkl~rung des Jet-stream pnanomens. BDW No. 12, 198-200 (10-63)

Preusche, W., 1952 Ein Modell zur Veranschaulichung der Vertikalbewegungen in der Jet-zone. BDW No. 38, 42-46 (4.2-177, 4G-lll) BIBLIOGRAPHY 91

Priestley, C.H.B., 1950 : On the dynamics of the general atmospheric circu­ lation. Aust. J. Sci. ~., Sere A., Phys. Sci., 3(1), 1-18 (2.1-75, 2.2-70, 4G-51)

Priestley, C.H.E., 1950 : Flow of momentum and mass across the high pressure belt of the earth's atmosphere. Nature, 165, 855-856 (8-42)

Proud, S., 1937 : Dpper winds at Kingston, Jamaica. GBPN No. 78, 26 p.

Queney, P., 1952 : Les ondes atmospheriques considerees comme aSSOClees aux discontinuites du tourbillon. Tel. 4, 88-111 (4G­ 112, 4.8-89, 7K-129)

Queney, P., 1953 La resonance interne du jet-stream et son rele dans la formation des cyclones. Ind. Acad. S~i., Bangalore, Proc., Sec. A., 37, 213-222 (4G-136)

Queney, P., 1953 Phenomenes de resonance et d'instabilite dans les ecou­ lements barotropes, avec application aux ondes atmosphe­ riques de grande echelle. Ann. de~~., 9, 185-226 (6.4-129)

Queney, P., 1954 Les grands mouvements de l'atmosphere. La Meteorologie, 4th Ser., No. 35, 195-207 (6.11-195)

*Radok, D., 1954 a Severe turbulence at high levels over New South Wales. MM 83, 48-52

Radok, D., 1954 b A comparison of geostrophic and observed upper winds. AMM No.7, 1-6

*Radok, D., and A.M. Grant, 1957 Variations in the high tropospheric mean flow over Australia and New Zealand. JM 14, 141-149

Raethjen, P., 1951 Das planetarische Zirkulationssystem. Annalen der Me­ teor., 4, 65-75. (3.3-110)

*Ramage, C.S., 1952 Relationship of general circulation to normal weather over southern Asia and the western Pacific during the cool season. JM 9, 403-408 (4.6-104, 4G-113, 5E-3l3)

Ramamurti, K.M., 1955 :A "jet stream" over northern India as revealed by a "Comet" debriefing report. IJMG 6, 277-278 (8.6-264)

Ramanathan, K.R., 1954 : Atmospheric ozone and the general circulation of the atmosphere. lAM, pp. 3-24 92 BIBLIOGRAPHY

Ramanathan, K.R., 1954 : On upper tropospheric easterlies and the travel of monsoon and post-monsoon storms and depressions. Pro­ ceedings, UNESCO Symp. on Typhoons, Tokyo, Nov. 9-12, 1954 (7.2-135)

Ramaswamy, C., 1956 : On the subtropical jet stream and its rille in the de­ velopment of large-scale convection. Tel. 8, 26-60

*Ramsey, B., 1955 Upper winds in the South-East Asia - West Australia re­ gion. MM 84, 372-376

Ratner, B., 1955 The high wind over Philadelphia, Pa., January 23, 1955. m~R 83, 31 (7.4-218)

Ratner, B., 1955 Winds and fallout: a climatological appraisal. US!1B, June 1955, 19 p. (7E-164)

*Reed, R.J., and F. Sanders, 1953 : An investigation of the development of a mid-tropospheric frontal zone and its associated vorti­ city field. JM 10, 338-349 (5.3-138)

Reed, R.J., 1955 A study of a characteristic type of upper-level fronto­ genesis. J~ 12, 226-237 (See also letters by Pothecary, JM 13, 316-317 and by Boville and Creswick, JM 14, 91­ 93)

*Reiter, E., 1957 a The layer of maximum wind. Final report, University of Chicago, Contr. Noas-55-262-C with Project Arowa, U.S. Navy

Reiter, E.R., 1957 b : Jet stream and jet aircraft operations. Navigation (Los Angeles) 5, 267-278

*Rex, D.F •• 1950 Blocking action in the middl,? troposphere and its effect upon regional climate. I. An aerological study of block­ ing action. Tel. 2, 196-211 (2.2-68)

*Riehl, H., 1948 a On the formation of typhoons. JM 5, 247-264

*Riehl, H., 1948 b Jet stream in the upper troposphere and cyclone forma­ tion. Tran~_kner. geophys. Un., 29, 175-186 (4G-15)

*Riehl, H., T.-C. Yeh and N.E. LaSeur, 1950 :A study of variations of the general circulation. JM 7, 181-194 (8-39, 48-52)

Riehl, H., 1952 Northern and Southern Hemisphere jet streams. Wea. 7, 388 (4.5-95, 4G-114) BIEL IOGRAPBY 93

Riehl, B., and C.O. Jenista, 1952 :A quantitative method for 24-hour jet­ stream prognosis. JM 9, 159-166 (3E-237, 4.3-81, 4G­ 115) (See correspondence L. Sherman and H. Riehl, JM 10, 231-232 (4.11-78))

*Riehl, B., and Collaborators, 1952 : Forecasting in middle latitudes. Me­ te~olo~cal Monographs, 1, No.5, 80 p.

*Riehl, H., and S. Teweles, 1953 :A further study on the relation between the jet stream and cyclone formation. Tel. 5, 66-79 (4G-127, 5.1-208) (See also Nyberg 1953)

*Riehl, H., 1954 a Jet stream flight, March 23, 1953. A~GB 7, 56-66 (5.11-89)

*Riehl, B., 1954 b: Tropical Meteorology. New York, McGraw-Hill (392 p.)

*Riehl, B., M.A. Alaka, C.L. Jordan and R.J. Renard, 1954 : The jet stream. Meteor. ~onographs, 2 (7), 100 p. (6B-201, 6.5-1)

*Riehl, H., and H. Maynard, 1954 : Exploration of the jet stream by aircraft during the winter of 1953. Univ. Chicago Dept. Meteor. Contr. N 189s-88360, Ii~al rep. (6.2-136)

Riehl, B. (letter) and S. Teweles, Jr., (reply), 1954 : Rainfall and vorti­ city advection. JM 11, 425-428 (6.3-81)

*Riehl, H., F.A. Berry and H. Maynard, 1955 : Exploration of the jet stream by aircraft during the 1952-1953 winter. JM 12, 26-35 (6.5-123)

*Riehl, B., and D. Fultz, 1957 : Jet stream and long waves in a steady rotat­ ing dishpan experiment : Structure of the circulation. QJru~s 83, 215-231

*Rigby, M., and M.P. Kramer, 1954 : Annotated bibliography on the tropopause. i~S 5, 488-548 (5D- -)

*Rodrfguez Franco, P., 1955 : Notas sobre las corrientes de chorro. Ravista de Geoffsico, Madrid, 14, 313-346 (8.6-204) ----

Rossby, C.-G., 1936 : Dynamics of steady ocean currents in the light of ex­ perimental fluid mechanics. Pap. Phys._Ocean. and Me­ teor., Cambridge, Mass., 5 (1) (4G-4)

*Rossby, C.-G., 1947 : On the distribution of angular velocity in gaseous en­ velopes under the influence of large-scale mixing pro­ cesses. BN~S 28, 53-68 94 BIBLIOGRAPHY

*Rossby, C.-G., and H.C. Willett, 1948 : The circulation of the upper tropo­ sphere and lower stratosphere. Scienc~, (108), 643-652 (4G-16)

Rossby, C.-G., 1949 : On the nature of the general circulation of the lower atmosphere. In : Atmospheres of the Earth and Planets, G.P. Kuiper (Ed.), Chicago, Univ. Chicago Press, pp. 16 -48 (10-65, 4G-27)

Rossby, C.-G., 1950 : On the dynamics of certain types of blocking waves. Chinese Geophys. Soc., Jour., Nanking, 2(1), 1-13 (2.5­ 69, 4G-53)

Rossby, C.-G., 1951 a : On the vertical and horizontal concentration of an­ gular momentum in air and ocean currents. I. Intro­ ductory comments and basic principles, with particular reference to the vertical concentration of momentum in ocean currents. Tel. 3, 15-27 (2.11-63, 4G-77)

*Rossby, C.-G., 1951 b : Uber die Vertikalverteilung von Windgesehwindigkeit und Schwerestabilitat in Freistrahlbewegungen der oberen Tropospnare. ~~GB 4, 3-23 (3.4-120, 4G-78)

*Rossby, C.-G., 1953 :A comparison of current patterns in the atmosphere and in the ocean basins. Un. Geodes. et Geophys. Int., Pro­ ces-Verbaux, Ass. de Meteor., Brussels, August 1951 (7.8-125) Rotch, A.L., and A.H. Palmer, 1911 : Charts of the atmosphere for aeronauts and aviators. New York, Wiley. 98 p., 24 charts (4E-3)

*Row, A.L., 1951 : Upper winds over Auckland. NZCN No. 78, 1 p.

Rubin, M.J., 1953 Results of recent observational studies of the Southern Hemisphere circulation. Syrup. on Use of Models in Geo­ phys. Fluid Dyn., Johns Hopkins Univ" Sept. 1-4, 1953 (5.6-119)

Rubin, M.J., and H. Van Loon, 1954 Aspects of the circulation of the South­ ern Hemisphere. JM 11, 68-76 (5.4-101)

Rutherford, G.T., 1954 :A profile of the jet stream, 9 August 1953. ~WA No. 7, 13-25 (7.4-143)

Rutherford, G.T., 1955 : Comparison of forecast winds with those reported by aircraft on high altitude flights. fu~ No.8, 33-36

*Rutherford, G.T., 1956 : The accuracy of forecast and found winds. fuWA No. 12 BIBLIOGRAPHY 95

Rutherford, G.T., 1956 : Clear air turbulence in Australia. AMM, No. 12, 61­ 71 (8.5-228)

Sato, T., 1951 Dynamics of the jet stream. PMG 2, 132-149 (4.2-108, 4G-79)

Satow, P.G., 1952: Meteorology and navigation. JIN 5, 203-222 (4.7-14)

*Saucier, W.J., 1955 : Principles~~~teorological analysis. Chicago, Univ. of Chicago Press (438 p.)

*Saucier, W.J. (letter) and H. Riehl (reply), 1956 : Exploration of the jet stream by aircraft during the 1952/1953 winter. JM 13, 312-314 (7.10-155)

*Saucier, W.J., ~al (a collection of papers), 1956 : Analysis and forecast­ ing of wind field near the tropopause. A. and M. ColI. of Texas, Final Report, Contr. No. AF 19 (604)-559 -

Saudek, V.M., and R.C. Eldredge, 1952 : Work carried out by the Southern California Soaring Association, Inc., in Phase II of the Mountain Wave Project, October 1951 - October 1952. Univ. Cal. Los Angeles, Dept. Meteor., Mtn. Wave_Proi" Contr. AF 19 (122)-263, Suppl. Rep. No.3 (5H-82)

Sawyer, J.S., 1949 The significance of dynamic instability in atmospheric motions. QJm~S 75, 364-374

Sawyer, J.S., 1950 Equivalent headwinds. Application of upper wind statis­ tics to air route planning. GBMR No.6, 20 p.

Sawyer, J.S., 1950 The movement of jet streams and the wind hodograph. ~~ 79, 357-358 (2.6-87, 4G-54)

*Sawyer, J.S., and B. Ilett, 1951 : The distribution of medium and high cloud near the jet streams. ~~ 80, 277-281 (3.4-195, 4G-8l)

SaW'fer, J.S., 1954 Day to day variations in the tropopause. GM 11, No. 92, 40 p. (5D-232) (See also 4G-80)

Sawyer, J.S., 1955 The free atmosphere in the vicinity of fronts. Q~ 12, No. 96 (5.5-113)

Sawyer, J .S., 1956 (Unpubl. talk) "Some new ideas on fronts". Wea. H, 124

Sawyer, J.S., 1956 The vertical circulation at meteorological fronts and its relation to frontogenesis. Proc. Roy. Soc. A, 234, 346-362 96 BrBLIOGRAPHY

Sawyer, J.S., 1957 Jet stream features of the earth's atmosphere. Wea, 12, 333-344

Schaefer, V.J., 1953 a Cloud photography project. Wwi. 6, 72-73 (5.1-226)

*Schaefer, V.J., 1953 b Cloud forms of the jet stream. Tel. 5, 27-31 (4G­ 128)

Schaefer, V.J., 1953 c : The use of clouds for locating the jet stream. Aer. 85, 599-602 (5.9-205)

Schaefer, V.J., 1955 : Atmospheric electricity associated with jet streams. Geophys. Pap. No. 42, Proc. Conf. Atmos. Elec., Geophys. Res. Dir., Air Force Cambridge Res~nter

Schaefer, V.J., 1955 : Jet streams, thunderstorms and project skyfire. A~GB 8, 265-282 (6J-332)

Schaefer, V.J., 1955 : Thunderstorms and project skyfire. N.Y. Acad. Sci., Trans., Ser. 2, 17, 470-473 (7.2-277)

*Schaefer, V.J., and W.E. Hubert, 1955 :A case study of jet stream clouds. Tel. 7, 301-307 (7.9-146)

Scherhag, R., 1948 Neue Methoden der Wetteranalyse und Wetterprognose. Springer Ver., Berlin (424 p.) (1-52)

Schmitt, W., 1952 Preliminary mean absolute topography 500 mb Southern Hemisphere 700 W- 120o E, summer 1951/52. Notos 1, 7-17 (4E-248)

Schmitt, W., 1952 Two intense polar-outbreaks in the southern oceans. Notos 1, 193-201 (4G-116)

Science Digest, 1951 : Jet winds rule the weather. Sci. Dig., 29, 65-66 (2.9 -77, 4G-69)

Science News Letter, 1953 : Track jet streams by cloud motions. Sci. N.L., 63, 83-84 (5.1-137)

Scorer, R.S., 1951 Clear-air turbulence over Europe. Wea, 6, 59-60 (2.6­ 80)

Scrase, F.J., 1954 Turbulence in the upper air, as shown by radar wind and radiosonde measurements. QJRMS 80, 369-376

Seilkopf, H., 1952 Modell der atmospnarischen Grosszirkulation. BOW 35, 68-71 (3.10-77) BIBLIOGRAPHY 97

Sekera, Z., 1949 The distribution of kinetic energy in certain steady barotropic currents. JM 6, 321-329 (2-79, 4G-28)

Sellick, N.P., 1950 High winds over Southern Rhodesia. Wea. 5, 67 (4E-267)

Serebreny, S.M., 1951 : Some preliminary considerations of the jet stream over Japan. Pan Am. Worid Airway$, Pac.-Alaska Div., Tech. Rep., No. 41 (4.3-120, 4G-82)

Serebreny, S.M., and E.J. Wiegman, 1953 : Characteristic properties of the jet stream over the Pacific, Case history No.1, Pt. 1. Ibid., Contr. N189s-90981, Tech. Rep., No.1, Nov. 1953 5.7-11)

Serebreny, S.M., and E.J. Wiegman, 1954?: Certain characteristic features of the jet stream and their application to airline opera­ tion. Met. Section, Pan ~. World Airw., Pac.-Al. Div., 37 p. (6.7-173)

Serebreny, S.M., E.J. Wiegman and W.F. Carlson, 1954 : Characteristic proper­ ties of the jet stream over the Pacific. Case history No.1, Pt. 2, ~, Contr. N189s-96835, Tech. R~. No.4, Sept. 1954 (161 pp.) (7~-124)

Serebreny, S.M., E.J. Wiegman and W.F. Carlson, 1954 : Characteristic proper­ ties of the jet stream over the Pacific. Case history No.2, Pt. 1, ibid., Contr. N189s-96835, Tech• ..E_~o No.2, Mar. 1954 (6.7-172). Also: Part 2, ibi~ Tech. Rep. 3, Aug. 1954 (157 p.)

*Serebreny, S.M., 1955 : The jet stream structure over the Pacific. Naviga­ tion, 4, 231-241 (7.5-125)

*Shaw, W.N., 1904 On the general circulation of the atmosphere in middle and higher latitudes. NWiR 32, 264-267

Shell Aviation News, 1953 : Cloud forms of the jet stream. Shell~News, No. 180, 4-6 (6.7-240)

Shell Aviation News, 1954 : Clear air turbulence and its allied phenomena. Shell Av. News, No. 192, 14-15 (6.7-222)

*Sheppard, P.A., 1951 : Recent advances in science, meteorology. The jet stream and related phenomena. Science Progress, 39, 483-495 (3.1-124, 3K-208, 4G-83)

Sheppard, P.A., 1952 : The general circulation of the atmosphere. Sci~r~., 40, 89-106 (3.6-9) 98 BIBLIOGRAPHY

*Solberg, H., 1939 Le mouvement d1inertie de l'atmosphere stable et son rele dans la theorie des cyclones. Proces-Verbaux, Me­ teor., Un, geod. geophys. inter., Edinburgh, Sept. 1936, II, 66-82

South Africa, Dept. of Transport, Weather Bureau, 1950 Upper winds in South­ ern Africa. Pretoria 1950. 282 p.

Starr, V.P., 1948 An essay on the general circulation of the earth's at­ mosphere. JM 5, 39-43 (7.8-128)

Starr, V.P., 1950 Geostrophic departures in the jet stream. Tel. 2, 233­ 235 (2.2-65, 4G-55)

Starr, V.P., and R.M. \Vhite, 1952 : Schemes for the study of hemispheric ex­ change processes. QJffi~S 78, 407-410 (3.10-116)

Starrett, L.G., 1949 : The relation of precipitation patterns in North America to certain types of jet streams at the 300 mil­ libar level. JM 6, 347-352 (2-80, 4G-29)

Stewart, C.D., 1924 : The measurement of upper wind velocities by observa­ tions of artificial clouds. GBPN No. 38, 15 p.

*Stiefelmaier, C.A., 1955 : Operational aspects of the jet stream. ~viga­ tion, 4, 227-231 (7.5-126)

Suda, K., 1955 On the cold wave of January 1954 in the Far East. Geo­ fis. Pura e Applic., 32, 159-169

Sutcliffe, R.C., 1940 : Rapid development where cold and warm air masses move toward each other. Syno? Div. Tech. Mem. No. 12, Air Min., Great Brit., 1940

Sutcliffe, R.C., and J.S. Saw-Jer, 1954 : Forecasting winds up to the 100 mb level by the contour-chart technique. PTMC, pp. 155-159

*Sutcliffe, R.C., and J.K. Bannon, 1954 : Seasonal changes in upper-air condi­ tions in the Mediterranean Middle East area. lAM, pp. 322-334

Teweles, S., Jr., 1954 : Jet-stream detail with respect to other meteoro­ logical factors. PTMe, pp. 188-192 (6.3-190)

Tillotson, K.C., and De V. Colson, 1954 : Wave-cloud formation at Denver. Wwi. 7, 34-35 (6.2-137)

Torrance, J.D., 1943 : Upper winds. So. African Air Force, Met. Section, Tech Notes No. 24, 7 p. BIBLIOGRAP~{ 99

T6th, G., 1933 : Szokatlanul nagy szelsebesseg a szabad legkorben Budapest fellett. Iaoj~ras, Budapest, 37, 91 (4G-3)

Touart, C.N., 1954/1955 : Jet streams fact and fiction. Air Univ. Quart. Egy. Maxwell Air Force Base, Ala. 7, 75-88 (7.11-174)

Treloar, H.M., 1948 : Extreme winds in high levels. Wea. Development and Res. Bull. Melbourne, 10, 15-18 (4G-17)

Treolar, H.M., 1954 : Geostrophic wind approximation in low latitudes. AMM No.7, 7-12

*Tun Yin, Maung, 1949 :A synoptic study of the onset of the summer monsoon over India and Burma. JM 6, 393-400 (3-87, 5B-262)

*Turner, H.S., 1955 Clear air turbulence and topography. Wea. 10, 294-297 (7.2-178)

Ulrich, K.O., 1954 go~n in der noheren Atmospnarebilden Gefahrezonen Tur den Luftverkehr. Umschau, 54, 577-580 (6.2-207)

U.S. Air Weather Service, 1951 : High-level isotach analysis. AWSM 105-26, 10 p. (3.1~58, 4E-220)

*U.S. Air Weather Service, 1952 : Bibliography on the jet stream. AWS Biblio­ graphy, No. 12, Mar. 1952, 9 p. (4G-117, 6B-136)

*U.S. Air Weather Service, 1955 : Winds over 100 knots in the Northern Hemi­ sphere. AWSTR 105-121 (67 p.)

*U.S. Air Weather Service, 1956 : Preliminary results of project cloud trail. AWSTR 105-132, 23 p.

U.S. Air Weather Service, 1956 : The Black Sheep system of forecasting winds for long-range jet aircraft. AWSTR 105-139, 48 p. (8C­ 79)

United States Navy, 1954 : Tables of winds and their aiding and retarding ef­ fect at 850, 700, 500, 300 and 200 mb. Part I, North Pacific Area; Part II, North Atlantic Area. NAVAER 50­ lc-526, Aerology Branch, Off. Chief Nav. Oper., 275 p. and 261 p.

U.S. Navy Bureau of Aeronautics, 1953 : Operational research into the detail­ ed structure of the jet stream. Project AROWA (TED-UNL­ MA-501.15), Second Quart. Prog. Rep., Jan. 1 - Anr. 1, 1953 (4G-129, 5.8-111) 100 BIBLIOGRAPHY

*U.S. Navy Bureau of Aeronautics, 1955 : Operational research into the detail­ ed structure of the jet stream. Ibid., Tech. Rep. No.2, Task 15, 59 p. plus appendix ----

u.s. Office of Naval Operations, 1952 : Practical methods of weather analysis and prognoses. U.S. Off. Nav. 0Q2., NA50-lP-502, 193 p. (5D-216) u.s. Weather Bureau, ---- : Monthly climatic data of the world *Univ. Chicago, Dept., Meteorology, 1947 : On the general circulation of the atmosphere in middle latitudes. BA~S 28, 255-280 (4G-6)

Vaisanen, A., 1954 Comparison between the geostrophic and gradient wind in the case of westerly jet. Geophysica, 4, 203-217

Van der Ham, C.J., 1954 : De straal stroom. Hemel on Dampkiring, 52, 201-210 (6.11-203)

Van Mieghem, J., 1939 : Sur l'existence de Itair tropical froid et de l'effet de foehn dans Itatmosphere libre. Mem. Inst. Roy. Meteor. Belg., No. 12, 32 p. (5D-105) Van Mieghem, J., 1950 : Sur la circulation transversale associee a un cou­ rant atmospherique. Tel. 2, 52-55 (6-37, 4G-56)

*Van Mieghem, J., 1951 : Hydrodynamic instabilityo Compendium of Meteorology, Boston, pp. 434-453

Van Mieghem, J., 1954 : Vorticity transport in the atmosphere. lAM, pp. 415­ 429

Vederman, J., and C.D. Smith, Jr., 1950 : The winter mid-troposphere circula­ tion near the North Pole. Bk~S 31, 197-205 (8-40)

*Vederman, J., 1954 The life cycles of jet streams and extratropical cy­ clones. BAMS 35, 239-244 (6.7-174)

Venkiteshwaran, S.P., 1950 : Winds at 10 km and above over India and its neighbourhood. Proc. Nat. Inst. of Sci. of India, 16, 19-27 (10-116, 2.6-88, 5.4-167)

Venkiteshwaran, S.P., and S. Yegnanarayanan, 1951 : Radar measurements of upper winds over Poona during the southwest monsoon. IJMG 2, 228-232 (3.7-146)

*Viaut, A., 1954 Quelques considerations sur Ie champ de pression et les perturbations du front polaire austral dans Ie sud sud­ ouest de l'ocean Indien. lAM pp. 290-301 BIBLIOGRAPHY 101

*Vuorela, L.A., 1948 : Contribution to the aerology of the tropical Atlantic. JM 5, 115-117

*Vuorela, L.A., 1950 : Synoptic aspects of tropical regions of the Atlantic Ocean, West Africa and South America. Helsinki, Univ., Meteorologian laitos, Mitteilungen, No. 67, 130 p. (2.4­ 27)

*Vuorela, L.A., 1953 : On the air flow connected with the invasion of upper tropical air over northwest Europe. Geophysica, Helsinki, 4, 105-130 (5D-244)

Vuorela, L., 1954 Ueber die Luftbewegung im Zusammenhang mit Vorstoessen tropischer Luft in hoeheren Schichten ueber Nordwest­ europa. Berlin, Freie Univ., Inst. fuer Meteor. u. Geo­ phys .. Meteor. Abhandl" 2, 152-172

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