28 



POLAR PROBLEMS 



annual movement of the sun causes the continents to heat in summer 

 and allows them to cool in winter, and the result is inblowing winds 

 toward the continents in summer, as in the case of the monsoons, 

 and outblowing winds in winter. In the case of land surfaces per- 

 manently covered with ice and contiguous to the open sea, like 

 Spitsbergen, Iceland, and the Antarctic Continent, there is a per- 

 manent tendency toward outblowing winds. 



Movement of Water 



The contrast between land and water is accentuated in many 

 regions by the second factor, movement of the water. In the North 

 Atlantic between Iceland and Europe the drift of the ocean is from 

 the equator toward the pole; and the water, especially in winter, is 

 much warmer than the mean temperature of that latitude, so that 

 the contrast between land and water is greatly accentuated. Along 

 the coast of Chile and Peru the surface of the ocean is drifting toward 

 the equator and is colder than the semi-tropical lands; so that here 

 again, in a different way, the contrast between land and water is 

 heightened. There are other similar cases, but these are the most 

 notable examples. 



Rotation of the Earth 



The third factor which interferes with the free exchange of air 

 between pole and equator is the rotation of the earth. Everyone is more 

 or less familiar with the rotation of the water flowing out from a bowl 



with an opening in its bot- 

 tom. On account of the ro- 

 tation of the earth, a similar 

 rotation is set up in the air 

 flowing toward each pole to 

 replace the colder air flow- 

 ing away. The circulation 

 taking place in the north- 

 ern hemisphere at a height 

 of about 4000 meters is 

 represented schematically 

 in Figure 2. In this dia- 

 gram the arrows point the 

 direction toward which the 

 air is moving. The direc- 

 tion of the circulation is 

 derived from direct obser- 

 vation combined with the 

 isobars at the height of 



Fig. 2 — Generalized circulation of the air around the 

 north pole at an altitude of 4000 meters. Derived from 

 observation, combined with the isobars of Teisserenc de 

 Bort. 



