The main factors that affect global circulation of air are the rotation of the Earth and the heat from the sun. There are three cells of air circulation in both the Northern and Southern Hemispheres. These three cells work together to create global air circulation.
The Hadley cells make up the two chunks of latitude nearest the equator. This is the area that gets most of the heat from the sun and extends to the 30-degree mark. The heated air near the equator rises, then flows south or north depending on the hemisphere toward the pole. The closer it gets to the pole, the cooler the air is, which causes it to sink. This circular motion happens in all three cells.
The second grouping of cells extends to 60 degrees latitude and is called Ferrel cells. The motion of these cells is forced by the other two sets of cells and produce westerly winds rather than vertical ones. This set of cells is the buffer zone between the hot Hadley cells and the cold Polar cells that encompass the poles.
The Polar cells extend from 60 degrees latitude and up. The northern and southernmost parts of these cells have high pressure, while the band of air nearest the Ferrel cells have low pressure, creating a front as the cold Polar air meets the moderate Ferrel air.