How are prevailing westerlies formed?
Prevailing westerlies form from convection and the Coriolis Effect. Due to unequal heating of the earth, air rises at the Equator and sinks at the Poles. That is, it would do that if the Earth were not spinning. Since it is, the rising and falling air patterns, called Hadley cells, are found between the Equator and 30 degrees N and S as the Trade Winds, between 30 and 60 degrees N and S as the Prevailing Westerlies, and between 60 and 90 degrees N and S as the Polar Easterlies. Right at those latitudes you find either rising or falling air. Prevailing westerlies blow diagonally, either from the SW or the NW depending upon whether it’s summer or winter (respectively).
