There are bands of high and low pressure around the earth. Air moves from high pressure to low pressure areas. This movement produces winds. Heat reaching tropical regions is much greater than in high latitudes because of the Sun's height in the sky and the depth of the atmosphere the rays cross. The general circulation of the atmosphere tries to redress this imbalance, with warm winds spreading excess heat polewards, to be replaced by cooler air returning from the poles. If the Earth was stationary, these winds would be fairly direct; but they are affected by the Earth's rotation, size and geography, as well as by seasonal changes in solar heating. In the northern hemisphere, moving objects such as air and water are deflected to the right as a result of Earth's rotation. They are deflected to the left in the southern hemisphere. This is called the Coriolis effect. Prevailing winds (those following a regular pattern) are arranged in a series of belts around the globe.

The cross section of this global circulation is in principle the same in both hemispheres, but in practice is slightly different. This is mainly because of the different distribution of land and sea. There is more land in the northern hemisphere and this pushes the meteorological equator to 5 degrees north.