Why are rain forests and deserts distributed in bands at certain specific latitudes?

Question

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Answer 1

The equator is hot, the air rises and creates a low pressure with rain.
The poles are cold, the air sinks and create high pressures with dry weather.
The air that rose over the equator, 'falls back' at about latitude 30 north and south. Two new high pressure belts are created with dry weather.
At latitude 60 north and south, between the tropical highs and polar highs, two new belts of low pressures are created with frequent rain.

It's in a nutshell. In reality, it's a bit more complex than that.

Answer 2

Because of the circulation pattern of winds. The atmosphere and ocean transport heat from the equator to the poles. The spinning of the earth interferes with this, causing complex patterns of air movement. These lead to bands of pressure that determine the way moisture is moved around, which in turn determines rainfall.