世界：沙漠 - Geografispel

Deserts primarily occur in two bands of latitude in the world. Moving both north and south from the equator, tropical air containing moisture slowly cools and drops its water in the form of rain. As the air continues to move away from the equator most of its moisture has already been dropped, and there is virtually nothing left by the time it reaches the location of the world’s deserts. Some places that would otherwise be a desert receive rain from the jet stream that transports moisture from the ocean.