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6.4: Idealized "average" global atmospheric circulation

Atmospheric Circulation

Global atmospheric circulation is influenced by temperature and pressure differentials, among several other factors. This section will cover atmospheric circulation in idealized terms. That is, circulation solely dependent on temperature-based fluid dynamics.

  • Atmospheric pressure patterns and atmospheric circulation cells

Air molecules in the atmosphere move following the laws of physics and fluid dynamics. Hot air will rise, just as cold air will sink. The processes that set the global circulation cells in motion are as follows:

1. On land, solar radiation heats up Earth's surface and surface atmosphere. This results in air molecules rising through the atmospheric column. It also creates a system of low pressure on the surface, since molecules float away, and form a system of high pressure at the top of the column as molecules bunch together.

2. In the atmosphere, air molecules are cooled at the top of the atmospheric column, and begin to sink. Like with the previous scenario, sinking molecules create a system of low pressure at the top of the column, and a high pressure system at the surface below.

3. Fluids move from high pressures to low pressures. In this case, at one point on earth molecules sink from the top of the atmosphere on to land as they are cooled, creating low pressure. At another point molecules that are rising due to higher temperatures on land are creating high pressure at the top of the atmosphere. This pressure differential results in molecules at the high pressure area at the top of the atmosphere to move towards the low pressure area at the top of the atmosphere. This is the same on land, where the molecules at the surface high pressure area move towards the surface low pressure area. This motion results in an atmospheric circulation cell.

  • Where do these cells form?

These atmospheric circulation cells begin in areas where solar radiation results in increased temperatures in land. On the equator, the intense solar radiation creates low pressure systems on the surface that initiate the circulation of air molecules. At 30N and 30S, the cooling molecules sink and form high pressure systems on the surface. These patterns are repeated every 30 degrees in both directions with the equator as the original low pressure area, alternating every 30 degrees thereafter.