Circulation Cells

So why don’t the poles get colder and colder, and the equator hotter and hotter? In nature, systems tend towards equilibrium, that is to say, nature doesn’t like differences, so the Earth system tries to even things out, and it does this by transferring heat from the tropics to the poles.

If the Earth was static, so not rotating, air would rise at the equator (because we know that hot air rises), move toward the poles, sink as it cools, then return the cooler air towards the equator.

In a non-rotating Earth, air would move in a conveyor between equator and poles

But the Earth’s rotation causes some complications, and because of the speed of the Earth’s rotation, we end up with three circulation cells in each hemisphere.

Each hemisphere has three main circulation cells, which redistribute heat from equator to poles (Click to expand)

These circulating cells not only transport heat from equator to pole, but also result in semi-permanent areas of high and low pressure due to the rising and descending parts of the circulation cells, which in turn lead to climatic zones. We’ll learn more about rising and sinking air, and high and low pressure later.

Semi-permanent pressure systems in the northern hemisphere

Semi-permanent pressure systems result in rainforests and deserts

Map of global climate zones (Click to expand)

For more information take a look at this article on the Global circulation system