Westerners often naively misunderstand the word “monsoon” to mean torrential rain, and indeed truly prodigious rains do fall during the rainy season in parts of India. But the monsoon is better understood as a vast system of seasonally-reversing winds. The English word
monsoon is derived from the Arabic word
mausin meaning “season.” Rather than cold and warm seasons experienced in North America and Europe, south Asia has very pronounced wet and dry seasons.
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| Sea Surface Temperature |
The equatorial waters of the western Pacific and Indian Oceans are like nowhere else on Earth. Warm water is pushed westward by Trade Winds across thousands of miles, accumulating in a
great wedge nearly 1000 feet deep called the Warm Pool. An area larger than Russia is always around 30 ºC (86 ºF). This huge pool of deep warm water evaporates like crazy, so that the region is perpetually both very hot and very humid. The juxtaposition of this humongous heat reservoir with the high cold Himalayas and Tibetan Plateau forms the heat engine for the great Asian Monsoon.
During the summer or southwest monsoon, solar heating of the high mountain terrain in the Himalayas and Tibetan Plateau causes the air to rise over a huge region. The rising air draws hot moist air up from the Indian Ocean and drives it into the mountains, wringing out phenomenal amounts of precipitation over south and southeast Asia.
In the winter or northwest monsoon, bitter cold air sinks from the mountains and flows southward across the subcontinent. During this time, the Sun is overhead in the Southern Hemisphere and monsoon rains move to Indonesia, Papua New Guinea, and Australia.
Monsoon rains are geographically structured by the hemispheric flow of moisture and the rugged topography of the Indian subcontinent. Rainfall in excess of 10 meters per year is typical in some areas of the Himalayan foothills!
Seasonally reversing monsoon winds control the cycles of productive vegetation, crops, and livestock across much of Asia. Billions of people depend on monsoon rains for food production. Farmers and pastoralists structure their lives around the seasonal winds and rains.
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| Annual Precipitation. SAS Ports for Spring 2026 Indicated by Red Stars |
