The unequal distribution of heat over the earth causes pressure differences in the atmosphere. Different parts of the earth receive varying amounts of radiation, with surplus in the tropics and deficit near the poles.

This leads to transfer of heat from one region to another by winds. The surplus heat from the tropics is redistributed polewards, preventing the tropics from progressively heating up and high latitudes from permanently freezing.

In middle latitudes, most daily weather variations are caused by advection or horizontal movement of air.