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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. Price 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.
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