224 WEATHER AND CLIMATE 



the tendency of the atmosphere in these belts is to take up 

 moisture rather than to deposit it. 



In the middle latitudes there is a belt of irregular winds 

 which have a prevailing tendency to move from west to east 

 or northeast. This general eastward drift of the air is 

 constantly being interrupted by great rotary air movements 

 having a diameter of from 500 to 1000 miles. These are 

 called cyclones and anti-cyclones. In this region of the 

 " westerlies," since the air tends to move from lower to 

 higher latitudes, an abundance of moisture is usually sup- 

 plied. 



Cyclones and Anti-cyclones. In the center of the large 

 storm areas called cyclones, the barometric pressure is 

 lower than that of the surrounding region, and so they are 

 marked " Low " on the weather maps. Into these low 

 pressure areas the air from all directions is moving. But 

 the winds from high pressure areas do not blow directly into 

 the center of a cyclone. On account of the rotation of the 

 earth, any wind that starts toward the center of the cyclone 

 area is deflected, in the northern hemisphere toward the 

 right ; in the southern hemisphere toward the left (page 219). 



For example, in the northern hemisphere the wind from a 

 point north of the cyclone center will be deflected to the 

 west ; the wind from the south will be deflected to the east. 

 Since all winds blowing toward the cyclone area veer to 

 the right of the cyclone center, they produce a great whirl 

 in a direction opposite to the movement of the hands of a 

 clock. (Figure 90.) In the southern hemisphere the cyclone 

 rotates in a direction with the hands of a clock. 



The rate at which the wind blows varies in different parts 

 of the whirl, but is never very great. As these are areas 



