WIND BELTS OF THE EARTH 



149 



temperature, due to the apparent movement of the sun 

 north and south v modifies the conditions in these wind 

 belts during the year. The planetary winds thus modified 

 are sometimes called terrestrial winds. 



74. Wind Belts of the Earth. Near the heat equator 

 where the air is rising there is a belt of calms and light 

 breezes called the doldrums. As the air here is rising 

 and cooling, thus having its capacity to hold moisture de- 

 creased, this is a cloudy rainy belt of high temperature in 

 which much of the land 

 is marshy and the vege- 

 tation so rank and lux- 

 uriant that agriculture 

 is exceedingly difficult. 



Extending north and 

 south of the doldrums 

 to about 28 of latitude 

 are belts in which con- 

 stant winds blow toward 

 the doldrum belt and 

 supply the air for the 

 upward current there. 

 In the northern hemi- 

 sphere these winds have a northeast to southwest direction 

 and in the southern hemisphere a southeast to northwest 

 direction. They are the most constant winds on the globe 

 in their intensity and direction, and are called trade winds. 

 Since they blow from a cold region to a warmer region, their 

 power to hold moisture is constantly increasing and clouds 

 and rains are not usual. The places where they blow are 

 dry belts and in them are found the great dry deserts of 

 the world. 



On the poleward sides of the trade- wind belts lie the 

 areas of high pressure already referred to. These are 



WIND BELTS OF THE EA.BTH. 



