Doldrums

The doldrums are the belt of light, variable winds and frequent calms near the equator, within the Intertropical Convergence Zone where the northeast and southeast trade winds meet. Surface pressure gradients are weak because converging air rises rather than flows horizontally, so the horizontal wind nearly vanishes while deep convection, towering cumulonimbus, and heavy showers dominate. Sailing ships could be becalmed here for days or weeks, the origin of the name. The belt is a few degrees wide and migrates seasonally with the thermal equator, lying mostly in the Northern Hemisphere over the Atlantic and Pacific.