1 86 ELEMENTARY SCIENCE 



I 



have some effect, and it is this effect which is portrayed 

 in Fig. 68. Remember (see Fig. 2) that the general con- 

 vection circulation of the atmosphere is poleward from 

 the equator for warmer air, and equatorward from north 

 and south for cooler air. Now if it were not for the 

 earth's rotation these great convection currents would 

 move due north and south, paralleling the meridians, 

 but, as it is, the rotation of the earth causes them to 

 bend (blow) westward in low latitudes (where rotation 

 speed is greater, and the water and land move a little 

 faster than the air) and eastward in high latitudes. In 

 other words, the atmosphere is bent westward at the 

 equator, and this bending has an effect which extends 

 clear up to the polar regions. So Fig. 68 represents what 

 may be called the basic directions of the world's winds. 

 But the air movements so determined are not so strong 

 but that they may be overcome by local conditions. 

 So they are often so modified and we may have even 

 violent winds which blow in a direction opposite to that 

 of the prevailing winds. Inasmuch as we live in the re- 

 gion indicated by the upper eastward-pointing winds, we 

 should expect our prevailing winds to be westerly, or 

 southwesterly; that is, from the west or south of west. 

 Is this the case ? 



Judging from the diagrams, you would expect the equa- 

 torial region to be, comparatively speaking, a region of 

 calms, the movement of the air being more upward than 

 horizontal. This is the case. There is a zone of equatorial 

 calms known as the doldrums. 



Also, note that the trade-winds north of the equator 

 blow from the northeast, while south of the equator they 

 blow from the southeast. 



