Convection Cells

Global winds move in a series of huge bands called convection cells. As you can see in Figure 13, these bands look like loops from the side. These bands are caused by temperature variations across Earth's surface. At the equator, for example, temperatures tend to be warmer than at other latitudes. Warm air rises at the equator, creating a low-pressure region. This warm air is replaced by cooler air brought by global winds blowing near the surface. Higher in the atmosphere, air blows away from the equator toward the poles. Similar convection cells cover large bands of latitude across Earth.

The trade winds are wind belts just north and south of the equator. In the Northern Hemisphere, they blow from the northeast to the southwest. The prevailing westerlies occur between 30° and 60° latitude in both hemispheres. These winds generally blow from west to east over much of North America. The polar easterlies extend from 60° latitude to the poles in both hemispheres. Trade winds, westerlies, and polar easterlies are examples of global winds.