Global Air Circulation

The major wind systems of the earth result because large masses of air around the earth's equator are forced to rise from the bottom due to surface heating. Cold air from high altitudes rushes in to replace the void thus created. The warm air from the equator travels towards the poles where it descends and returns towards the equator along the surface of the earth. This system is shown in figure below and it is influenced by two factors:

1) The heat retention of airmasses is not the same as for oceans. You already know that land cools as well as heats up more rapidly, and land masses are not distributed uniformly.

2) A force associated with the earth's rotation deflects the air flow in the northern hemisphere to the right and in the southern hemisphere to the left.