POLAR INFLUENCES ON WORLD WEATHER 



31 



about 75° N. and longitude between 155° and 175° E. by means of 

 kites flown from the ship Maud. They show the following mean dis- 

 tribution of temperature, with heights, on days when it was possible 

 to fly kites (see also the dotted curve in Figure 4 and theJuUcurve in 

 Figure 5) : ^x 



Altitude (meters) o 136 272 1000 1500 2000 \ 



Temperature (degrees C.) -284 —28.9 -22.8 -20.3 -21.7 -24.0 



On quiet days the surface temperature was lower, averaging - 32.4° C. 



Cold Waves and Polar 

 Fronts 



2000 



1500 



1000 



500 



-35 



Fig. s — The temperatures at different heights 

 in the Arctic Sea in winter as observed by H. U. 

 Sverdrup by means of instruments lifted by kites 

 flown from the ship Maud (shown by the full 

 curve). The broken curve in lower elevations 

 shows the temperatures on calm days. (From 

 paper cited in footnote 4.) 



Both sets of observations show 

 that there is in the polar regions 

 in winter a very cold stratum of 

 air near the earth's surface, with 

 a warmer stratum above at a 

 height of 500 to looo meters. 

 Above that height the tempera- 

 ture decreases again. This surface 

 stratum has . very little motion ; 

 and calm, serene, clear weather is 

 characteristic of the polar winters. 

 The cold surface air undoubtedly 

 flows out slowly, but this cannot 

 be the origin of the fierce cold 

 waves that occasionally sweep 



southward into temperate latitudes. In the United States these 

 cold waves progress with the velocity of a rapid express train. They 

 move much more rapidly than the surface winds along any part of 

 their path. Their rapid progress is in the upper air at some 2000 

 to 8000 meters above the earth's surface, and the^air is descending 

 as it progresses southward. This is evident from the fact that the 

 air is very clear and the humidity low. 



My study^ of the observations made in the free air at St. Louis 

 in 1 905-1 907 by the staff of the Blue Hill Meteorological Observatory 

 shows that these cold waves extend to heights of about 10 kilometers. 

 It seems clear that they are not the result of the surface air of the 

 Arctic moving southward but owe their origin to the cold upper air 

 which has been chilled by radiation from the air itself. 



The observations of Dr. Sverdrup showed an average temperature 

 of —24° C. at 2000 meters (Fig. 5). If this air descended in the 

 Arctic region it would heat by compression and have a temperature 



5 H. H. Clayton and S. P. Fergusson: Exploration of the Air With Ballons-Sondes at St. Louis 

 and With Kites at Blue Hill, Annals Astron. Observ. of Harvard College, Vol. 67, Part I, 1909. 



