What is global circulation? | Part Two | The three cells

Global circulation redistributes heat from the equator to the poles. The Earth's rotation and land/ocean distribution create a complex three-cell circulation pattern in each hemisphere, unlike the single cell that would exist on a non-rotating, simple landmass.

Hadley cells are the largest cells, located at the equator. Warm, less dense air rises to about 18 kilometers, spreads poleward, gradually cools, sinks, and then flows back to the equator at the surface.

Polar cells are the smallest. Cold, dense air descends in the polar regions, flows at low levels towards 60-70 degrees latitude, warms and rises, and then returns to the poles at high levels.

Ferrel cells are located between the Hadley and Polar cells. Unlike the other two, they are not temperature-driven but flow in the opposite direction, acting like a gear between the other cells.

These circulating cells transport heat and create semi-permanent areas of high and low pressure, leading to distinct climatic zones. Rising air creates low pressure areas with significant rainfall (e.g., rainforests near the equator, the UK), while descending air creates high pressure areas with largely clear skies and little rainfall (e.g., desert regions like the Sahara and Antarctica).