Monsoons

Indian Monsoon

The Indian monsoon is a wind that blows seasonally over India and the land areas surrounding India. The winds blow in different directions at different times of the year. The monsoon winds blow from the southeast from April to October. From November to March they blow from the northeast. The monsoon brings rains when it blows from the southwest across the warm waters of the Indian Ocean. Hundreds of millions of people depend upon the rains it brings. When it blows from the northeast, dry air prevails to create the dry season. Monsoons also occur in northern Australia, the northern and eastern coasts of Asia, some of the Pacific Coast of North America, South America, and Sub-Saharan Africa. In addition, the Indian Ocean has monsoon areas that include parts of the east coast of the African continent.

Differences in the temperatures on land and sea cause the monsoon winds. The temperature differences occur because the heat transfers in the ocean happen in a different manner than the heat transfers on land. In the ocean, sunlight heats the water to a depth of about 64 ft. (50 m.). Winds and wave action churns the ocean waters and as it heats and cools with annual seasonal changes energize or slow wind action. The heating and cooling of the land and waters of the Indian Ocean cause the temperature differences. Sunlight striking the surface of the Earth heats it to much higher temperatures than it does ocean water. As the heated air rises, a large area of low pressure caused by the rising air is formed. The relatively cooler and denser air that blows across the Indian Ocean flows in to fill the low-pressure areas with its heavier air. At the same time, the relatively cooler air is laden with moisture, but is heated over the land so that the moisture rises is cooled at high elevations, condenses, and falls as rain over the land. During the winter, the land is cooler than the Indian Ocean, so as the air over it rises to form low-pressure areas the denser land airflow from the land into the low pressure over the waters of the Indian Ocean.

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