Weather and climate
Monsoons
Billions of people depend on the arrival of the monsoon every summer to the parched lands of southern Asia. Monsoons are winds that reverse direction each year. This happens when there are great differences in temperature between the oceans and the land. Cool, dry winds are replaced in the summer by warm, moist winds from the Indian Ocean. Heavy rains then arrive.
How monsoons occur
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During the winter, cool, dry air flows southwards from northern Asia. For six months, India has a drought as there are no moist winds blowing in from across the Indian Ocean (1). Eventually, the land heats up in the summer sun and the air above it becomes warmer than the air over the ocean. Moist air now flows in, bringing heavy rains (2).
Consultant: Ian Fairchild