Monsoon

Monsoon (Arabic, mauism, “season”), wind that changes direction with the change of seasons. The monsoon prevails mainly in the Indian Ocean. It blows from the south-west, generally from April to October, and from the opposite direction, the north-east, from October to April. The south-west, or summer, monsoon occurs when warm, moist air from the Indian Ocean flows onto the land, and is usually accompanied by heavy rain in areas of India and South East Asia, constituting the dominant climate event of the area. The north-east monsoon occurs in India when cold, dry winter air flows out of the interior of Asia from the north-east and brings the cool, dry winter season.

The appearance of this wind pattern over geological time has been linked, through sedimentary evidence, to the uplift of the Himalaya and the Tibetan plateau as the Indian subcontinent began to collide with the Asian crustal plate about 20 million years ago. The northern land mass was high enough by about 6 million years ago to cause air rising from the southern land mass to be replaced by the monsoon, establishing this wind pattern. Monsoons, in weaker form, also occur in other parts of the world.

Monsoons can be beneficial as well as devastating. After six months of drought, the rains are welcome. After several months of the monsoon, however, extensive flooding may occur.