High pressure and mountains

Why deserts form

Descending air north and south of the tropical zone produces almost permanent areas of high pressure across the subtropics. Met Office This produces almost cloud-free skies virtually year-round, giving rise to deserts. Met Office

Desert climates are extremely dry, and their cloudless skies lead to large temperature swings. Met Office Deserts have some of the hottest temperatures on Earth, but many will drop below freezing at night. Met Office

The trade winds in two belts on the equatorial sides of the Horse Latitudes heat up as they move toward the Equator. USGS These dry winds dissipate cloud cover, allowing more sunlight to heat the land. USGS Most of the major deserts of the world lie in areas crossed by the trade winds. USGS

Rain shadow deserts are formed because tall mountain ranges prevent moisture-rich clouds from reaching areas on the lee, or protected side, of the range. USGS As air rises over the mountain, water is precipitated and the air loses its moisture content. USGS The Andes mountain chain causes a rain shadow effect that results in minimal precipitation in the Atacama region of Chile. NASA

The same idea shows up in more than one place: dry air, whether it is sinking over the subtropics or losing its moisture over a mountain range. The types page sets out the USGS groups.