402 CLIMATE 



Winds modify the temperature of a region because to a certain 

 extent they carry their temperatures with them. Thus the 

 north wind in general carries cool air southward and lowers the 

 temperature of southern regions and the south wind in general 

 carries warm air northward. Every one living on the coast 

 knows that a breeze blowing in from the sea means a lowering of 

 temperature on the shore. Winds or horizontal movements of 

 the air near the earth are an important factor in climate. Winds 

 affect human beings very greatly. Dead calms are enervating, 

 gentle winds are invigorating. On hot days when no air is 

 stirring, the heat is oppressive and unfits one for hard active 

 work; on days when a gentle breeze or a high wind is astir, 

 the heat, although just as great according to a thermometer, 

 is less oppressive and does not seriously interfere with work. 



Winds, as learned on page 27, are caused by differences of 

 temperature in different parts of the earth. The tropics are 

 more strongly heated than temperate regions, and the air over 

 the tropical lands expands and rises and creates a low atmos- 

 pheric pressure in the region which it leaves. Cooler air from 

 the temperate regions where the pressure is higher rushes into 

 the tropical belt. This cool air is quickly warmed and rises, 

 and its place is in turn taken by cooler air from the temperate 

 regions. In this way permanent air movements or winds are 

 created. 



If A (Fig. 270) represents the north pole, E the temperate 

 areas, CD the strongly heated tropical areas, and B the south 

 pole, we can trace the path of the outflowing warm winds and 

 the inflowing cold winds. The warm air over the tropical area 

 CD is pushed up by the denser cold air which flows in from 

 EE. This cold air is warmed and is in turn pushed up by 

 other cold air from the north and the south. In this way there 

 is created a permanent horizontal flow of air toward the poles 

 in the upper atmosphere and a permanent horizontal flow of 



