Monsuns

Monsuns are seasonal wind systems that bring distinct wet and dry seasons to large parts of the tropics and subtropics. The term monsoon comes from the Arabic mausim meaning season, and the concept describes a class of climate phenomena driven by the differential heating of land and sea and the resulting seasonal shifts in atmospheric circulation.

In summer, intense heating over continental regions lowers surface pressure and draws moist air from adjacent oceans toward land, producing heavy rainfall in many monsoon regions. In winter, cooler, drier air moves from land to sea, leading to a retreat of rain in the interior and a dry season in affected areas. The timing and intensity of monsoon rainfall are influenced by factors such as the monsoon trough, the position of the Intertropical Convergence Zone, sea-surface temperatures, and regional atmospheric patterns.

Major monsoon systems occur in several regions. The South Asian monsoon, including the Indian subcontinent and parts of Southeast Asia, is one of the most well-known and highly studied. The East Asian monsoon affects China, Korea, and Japan. The African monsoon governs rainfall over the Sahel and parts of equatorial Africa. In the Americas, the North American monsoon affects the southwestern United States and parts of Mexico, while the South American monsoon system influences parts of the Amazon basin and adjacent regions. In Australia, the northern region experiences a tropical or Australian monsoon with a pronounced wet season.

Monsoons are subject to substantial interannual and decadal variability, influenced by phenomena such as El Niño–Southern Oscillation, and are sensitive to broader climate change, which can alter their timing, duration, and intensity.