WINDS 



4>3 



air toward the equator in the atmosphere just over the earth. 

 Horizontal movements of air over the surface of the earth are 

 called winds ; similar movements in the upper atmosphere are 

 called currents. The winds which blow from E to the equator 

 are called trade winds, because their persistency and con- 

 stancy make them 

 of service to trading 

 vessels. 



Much of the air 

 which starts on a 

 poleward journey 



FlG ' 



Diagram of air currents. 



does not reach the 



pole, but sinks back to earth when it reaches latitude 25 35, 

 that is, as far north as Florida and South Carolina in the 

 northern hemisphere. This is because it slowly loses its heat 

 and becomes cool and heavy enough to sink to the earth. 

 Roughly speaking., there is a vertical rising of air at the equator, 

 air currents toward the poles in the upper atmosphere, vertical 

 falling of air at 25-35 north, and winds toward the equator 

 from north and south. 



The direction of the trade winds and air currents is not due 

 north and south, but is obliquely toward the west. This 

 shifting from the true north-and-south direction is caused by 

 the rotation of the earth on its axis. 



Other well-recognized winds whose course is not easy to trace 

 are the westerlies, which blow obliquely eastward toward 

 the pole in middle and high latitudes. 



In addition to the trade winds and westerlies which flow con- 

 stantly over the earth, there are irregular variable winds which 

 spring up at different times and places and under different cir- 

 cumstances, such as day and night breezes, mountain and valley 

 breezes, land and sea breezes. Just as breezes may at one time 

 blow from ocean to land and at another time blow from land 



CLARK INTRO. TO SC. 26 



