MONSOONS

The seasonal winds of south-west Asia known as monsoons are asso­ciated particularly with India be­cause of the tremendous effects they have on the lives of the in­habitants. The winds are drawn to India by changes in the tempera­ture of the great land mass. A good monsoon season with plenty of rain means a comparatively good supply of food. A bad monsoon with little rain means a bad rice crop and, perhaps, starvation for many millions.

Monsoon comes from the Arabic mausim, meaning season. The summer season monsoon is a great inrush of moisture-laden air from the ocean. The winter monsoon blows from the land to the sea.

In India there are three seasons: the hot dry season from March to June; the hot wet season from June to November; and the cool dry season from  December to March. During the hot dry season the great plains of northern India become like a furnace and a region of low pressure develops.

By mid-June, the pressure is low all the way to the Equator and draws the south-east trade winds to India, filled with water-vapour as they cross the Indian Ocean. When they meet the hot dry air over India, violent thunderstorms result, followed by steady rain in July. By November India has received three-quarters of its annual rainfall.

Then the land mass cools and the high pressure attracts the north east trade winds. These bring no rain to India except to the Coromandel Coast and Ceylon, where the rainfall in late Septem­ber is heavy, because the winds have picked up water vapour as they move across the wide expanse of the Bay of Bengal.