Meteorologists – why does each hemisphere have 3 climate/wind cells instead of 1 big one?

Question

Meteorologists – why does each hemisphere have 3 climate/wind cells instead of 1 big one?

In: 2

Answer 1

The coriolis effect.

Let’s follow a bit of air rising at the equator, where it’s really hot. The Earth is spinning, and the air spins with it, so it has quite a bit of momentum. That doesn’t matter for now, but if the rising air heads north or south, the speed of the planet’s surface diminishes. Air however is slippery, and starts to slip ahead. Seen from the surface, it looks like the air is curving. Eventually it has curved so much that it’s blowing perpendicular to the Earth’s surface, which means there’s no more force pushing it polewards. This ends the climate cell, and the air sinks and is sucked back towards the equator, where the rising air created low pressure. The rotation speed and size of the Earth works out to three climate cells per hemisphere. In comparison, the planet Jupiter has 18, and Mars has one.