THE ENGINE OF THE AIR 



153 



tinue its northward drift as a high west wind, until further 

 cooling at the pole again causes it to sink. There are also 

 differences in radiation from the ocean and the continental 

 land masses and the reflection of radiation from ice, which 

 disturb the symmetry of this elementary circulation. 



The net result — short of a technical explanation — is that 

 the simple engine becomes a three-zone system of air be- 



HIGH 



LOW 



HIGH "^^'^^^ 



NORTH POLE ** 



.^ — ?vP 



LOW i< r ^Q*-^ ^ FRONT 



PREmiUNG IVESTERLfES 



/ / 



DOLDRUMS 



The final result of cellular meridional circulation on a rotating earth; Con- 

 vection near the Equator, a clear zone of descending air nnotion north of it 

 In about Latitude 30°, and cloud nnasses and rain at the polar front in Lati- 

 tudes 50-60° N. 



tween pole and equator. There is a trade-wind zone with 

 rising air near the equator, a polar-front zone with falling 

 air at the pole, and a separating zone in middle latitudes. 



