up to at least 13,000 feet. Likewise in autumn northerly winds 

 prevail from 3,000 to 13,000 feet. 



Observations made during the Wordie expeditions to northwest 

 Greenland in 1937, and to the Canadian Arctic in 1938, confirm 

 other observational data to the effect that the highest wind veloci- 

 ties are found at or immediately below the tropopause. The height 

 of the tropopause for one observation was found at 37,750 feet, 

 while the maximum wind velocity occurred at 32,150 feet. The 

 maximum velocity at this elevation was 34 m. p. h. The height of 

 the maximum wind velocity and likewise the height of the tropo- 

 pause was found to vary with the surface pressure. During the 

 presence of low pressure areas the maximum velocity occurred at 

 lower elevations, from 26,250 feet to 31,150 feet, and in high pres- 

 sure areas from 32,800 feet to 37,750 feet. In comparison with 

 data collected at other seasons the maximum velocities are found to 

 occur about 10,000 feet lower in the winter than in the summer. 



WIDELY DIFFERENT SYSTEMS 



A comparison of the winds-aloft regimes at Tikhaja in Franz 

 Joseph Land and at Tromso, Norway, affords a good example of 

 the widely different systems that exist on either side of the Atlantic 

 Arctic Front. Tikhaja, near the 80th parallel, lies to the north of 

 the front and its wind system is largely governed by the Polar 

 Anticyclone. Tromso, on the seventieth parallel, lies south of 

 the front and its wind circulation is governed by the Icelandic 

 Low. However, the wind system at Tikhaja is also influenced by 

 the latter low. Northeasterly winds are prevalent up to 13,000 

 feet at Tikhaja for all seasons except summer. In summer at the 

 surface 32 percent of the time it is calm and 34 percent of the time 

 the winds are north to east. Above the surface layer, in summer, 

 there is no marked prevalence from any direction. The Icelandic 

 low pressure system is practically nonexistent in the summer and 

 the Polar Anticyclone is weak. For all seasons at Tromso, south 

 of the front, there is a prevalence of southerly wind, shifting to 

 southwesterly above 3,000 feet and extending up to 10,000 feet. 

 At 13,000 feet there is no direction of greatest frequency. Veloci- 

 ties from 1,600 to 10,000 feet are slightly higher at Tikhaja, the 

 average being between 12 and 18 m. p. h., while at Trom^^v^ aver- 

 ages are from 10 to 18 m. p. h. At 13,000 feet the average is 

 slightly higher at Tromso. 



In the winter the surface winds at Dikson Island, in the Kara 



108 



