Hadley cell
Heating of the earth near the equator forces upward motion and convection along the monsoon trough or intertropical convergence zone. The divergence over the near-equatorial trough leads to air rising and moving away from the equator aloft. As air moves towards the mid-latitudes, it cools and sinks leading to subsidence near the 30° parallel of both hemispheres. This circulation known as the Hadley cell forms the subtropical ridge. Many of the world's deserts are caused by these climatological high-pressure areas. Because these anticyclones strengthen with height, they are known as warm core ridges.