244 MONTHLY WEATHER REVIEW JULY 1934 UPPER-AIR WINDS OVER NORTHERN ALASKA DURING THE INTERNATIONAL POLAR YEAR, AUGUST 1932-AUGUST 1933, INCLUSIVE By LOYDA. STEVENS Weather Bureau, Washington, D.C., July 19341 The United States Weather Bureau has prepared some three stations, Point Barrow, Nonie, and Fairbanks; being 25,000 pilot-balloon suinmary forms for the International given for all standard levels by months and for the year. Polar Year Commission, on which are entered the data The monthly resultants are shown for levels up to G kilo- from all Weather Bureau pilot-balloon stations, including meters insofar as data are available, mid the annual 1 in Puerto Rico rind 4 in AlRSkft for the period, August values are given for the two additional levels of '7 and 8 1932 to August 1933, inclusive. Since the International kilometers. In sonie cases the number of observations - 6000 ARROWS FLY 5ooo WITH THE- WIND LENGTHS OF 4000 ARROWS 3000 REPRESENT 2000 VELOCITIES IN METERS PER 1500 SECOND- 1000 VELOCITY SCALE 500 ouS"R (M3.L) FIGURE1.-Resultant winds at Fairbanks, Nome. and Point Barrow, Alaska Coniniission was espec,ially interested in observations in for an individurtl month was sinall, causing apparent and near the polnr re,,oions, the Wea.ther Bureau estnh- inconsistencies and irregularities, but in FenFral the air lishe.d, and maintained for the greater portion of the movement over this areti is believed to be inhcated quite Po1a.r Year, a spe.cia1station tit Point Barrow, the north- accurately in figures 1 and 3 011 which the resultants ernmost point of land in Alnska,; latitude 71'23' X., have been drawn. longitude 150O17' W. Along with other iniportsnt, East,erly winds prdoniinnte helow thrce ldoniete,rs at matters, pilo t-belloon observations were t.nkeii twice all t,liree stations during t,he grmter portloii of the yenr. daily, weat'hcr permitting, from September 14, 1932, to This m8.y he attributed to the influence of the Aleutitm August 11, 1933, inclusive. During t'his period 5SO LOW, the doriihnnt pressure nrea in that region, usunlly flights were made; or 58 percent of the total scheduled. cmtered to the wcst or southwest of Alaska. During Of these, 4'73 reached 1,000 meters; 3'76, 3,000 meters; niid-summer howeyer, the Aleutian LOW is rather weak 108, 5,000 meters; srid 15, 10,000 niebers. The highest 2nd a stronger nrea. of high pressure. builds up. over the single fllght was made on July 9, 1933, when fin altitucle. north Pacific,. The effect,of this pressure distribution is of 12,500 meters was attained, at which level the wind refle,ctecl in the westerly resultar?t,s which prevail during was NNE., 15 meters per second. The highest velocit,y June, Jdy, nnd August. Above 3 kilometers the result- recorded during the entire period was 41 meters per sec- ants are in general from the west. ond from the west on October 7, 1932, at an n.ltitude of It will be noted that the shift from enst,erly to westerly 10,350 meters. resultant direc,tions occiirs between 2 and 3 kilonieters at RESULTANT WINDS Point Barrow and Fairbanks, and between 5 and 6 ldo- Since resultant winds, based upon a sufficient nunibcr meters at Kcme. This is probnbly dce to t,he fact that of observations, indicate the tme mass movement of the t8hecenter of the Aleutian LOW is 011 t,he average nearer atmosphere, they are shown here in some detd for the to Nonie thn.n to the other two points. Unauthenticated | Downloaded 09/26/21 08:35 AM UTC JULY 1934 MONTHLY WEATHER REVIEW 245 8000 5000 3000 3000 2000 2000 1000 Unauthenticated | Downloaded 09/26/21 08:35 AM UTC 246 MONTHLY WEATHER REVIEW JULY 1934 The resiiltant wind directions conipare favorably with by dividing the sum of all velocities by tlie tot,al number the avcrrtge pressure maps for the North Polar regions of observations. shown by Sir Napier Shaw in volume 2 of his Manual of Meteorology .' TABLEl.--Si(oimary of atwaye inind rvloofics arid number of Resultant velocities are, for the most part, rather o hserimt ious-Polar J'COT, lSS,!-s'S light, and irdicate less ntmospheric inovcment hcrc t,li~~i in the midc! le !tit itud es. WIND ROSES Areraee Nnrnher relocity Averagevelocity In figure f;, wind roses nre given for the Polnr Tcnr PS :r$,,E- a whole. ~~ It will be noted tlint for the lower levels the most fre- Surfare.. ..... ..... .~... 1.5 64 1 3.5 5.0 580 I,IXI0mrtcrs~~..~.... ~... 6.2 623 9. 2 Ji3 quent wiiitl directions ohswved are between E. niid SE. 2.W)O nwlsrs .... ~.... ... 7.3 517 7. 7 ??0 R. 5 39 I 3.1~0ruet.ers...... ~~ ..... 7.9 354 181 8. 7 276 at Fairbanhb, E. or ENE. at Point B:irrc;w :,id between 5,(100 meters ............. 11. 1 153 4i 9. 1 106 N. arid NE. tit Nome. A shift to westerly prevniling 5,oOO mrtrrs ~...-........ I?. S 23 10. 4 3 winds occurs on the average at the height of almit 2 kilometers at Fairbanks, and between 2 and 3 kilcnieters It will be not.ed t1in.t the average velocit,ies increa,se at Point Bnrr.ow. At Nome, it occurs much higher, be- rapidly from the surface to 1,000 meters at, all stahions. twee:i 4 and 5 kilometers. At 5 kilometers the most Above 1,000 met,ers, at Fairbanks, there is a gradual tip 8,000 a ARROWS FLY WITH THE WIND increase in vclocit,y to meters; at Nome, LENGTHS OF ARROWS REPRESEINT VELOCITY gradual increase to 3,000 meters, t,he,n a decrease and a.n ELEV. FAIRBANKS inc.rease n.ga.in at 8,000 meters; at Point Barrow, a METERS OBS.) decrease from 1,000 t,o 3,000 niet,ers and an increase 8000 pk2-3- again from 3,090 to 8,000 met'ers. The drop in velocity at 5,000 meters at Nome and at 3,000 at Point Barrow, coincides closely with blie average height at which the 7000 -\& 7000 =-38 shif t occurs from easterly to westerly prevailing winds. A simi1n.r drop in ve.locit,y is not evident) at Fairbanks, 6000 - 000 but the incren.se in velocity between 2,000 and 3,000 -? meters (at, which height the shift occurs) is notably less t1in.n the clinnge betwe.en ot,lier levels. 5000 \ 10- Tlic extremely low veloc,ities and frequency of calms at 1i'airb:inks we believed to be due in part to local 4000 - 4000 t.opography. It shoulcl be stated, however, in this con- I6i- nection, tlint t,he average velocities for dl levels for these \ three stations, are 3 bo 3 meters per second less than t,hose 3000 276- 3000 for rdot,-bn.lloon stnt.ions in t,he nort,hern Dart of t,he <Tiitkc1 States. 2000 i' 2000 From the monthly average velocities, which have been 391 computed but arc i;ot s1ioU.n here, it) nitty be stated that velocities tire highest during the winter months and low- !SO0 - 1500 441 est during the suninier months, but the seasonal varin- tion is relatively small as conipnred with stationq in the 1000 A IO 00 middle la tit des. 473 VELOCITY FREQUENCIES 500 L- 500 5 54- In (able 3 tlie percentage frecluencies of different ve- locities are shown for standard reloci!y groiips, for the SUR SUR months of .Jnnuary and July 1933 and for the Polar Tear. (14 s 0 u -.?Iao(MSL).. V'ELOCITY SCALE IN METERS PER SECOdD At the surface, more than S5 percent of all recorded velocities are lietmeen calni and T nieteis per second; tlie S 14 frequent direct8ionsrecorcled are a.t E'a~rba~~hs, reiiininder falling in the group of to meters per sec- W. WNW. ond. At 1,000 meters the percentage of velocities of 7 Ht, Point Barrow and SW. at Nome. At 8 kiloiiieters tbt? most, freqiicnt directio~isare W'SW. at Fairbniiks nnd meters per second or less for the three stations combined, Pcint Borrow and SSJ?". at Nome. However, only G decrenses to 53 percent while those between 8 and 14 iiieters per second increase to approxiiiiately 33 percent ohserva.tions wcrc iiindo r,t 8 Idometers at, Nome, mid and those between 1.5 and 21 111 rs per second amount there,fore t,l!e wid rcisc for this le,vel probably is not to appro.\iiiiittelg 6 percent. At 5,000 meters tlie per- representativ e of averaye conditions. In general highest velocities occur with the prevailing centage of velocities between 0-7 and 8-14 meters per second are 15 percent and 4 1 percent, respectively, and directions, but the winds of all directions have nea.rly the those between 15-21 and over 21 are 11 percent and 3 same value. percent, respectively. AVERAGE VELOCITIES (MPS) It is apparent from the table that in general a greater Average velocities for the Polar Pear together with percentitge of velocities i~llwithin the higher brackets the number of observations on which these averages a.re during January than during July, and also that there is a based are given in table 1. These values were obtained gradual increase with height of the percentage of velocities 1 Sir Napier Shaw, Manual of Meteorology, vol. 2, pp. 216 to 268. of 15 meters per second and over. 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