The Hadley cell is the main driver of tropical circulation. Air heated at the ITCZ rises, moves poleward in the upper troposphere (anti-trades), descends at ~30° creating subtropical highs, and returns to the equator as trade winds.
Subsidence at 30° generates the great deserts (Sahara, Arabia, Kalahari). Climate change is expanding the Hadley cells ~0.5° latitude per decade, pushing subtropical aridity toward the Mediterranean.