Back to #1347 - Neil deGrasse Tyson.
Why Does the Mojave Desert Sit Near 30 Degrees North?
Air rises at the equator and builds clouds, which is why the Amazon is among the rainiest places. The same circulating cylinders of air descend about 30 degrees north and 30 degrees south, and descending air does not make clouds. That puts the Mojave Desert, the Sahara Desert, and the Gobi Desert near 30 degrees north.