MONSOON IN INDIA

                                 MONSOON IN INDIA

Mechanism of the Indian Monsoon

The climate of India may be described by one word namely "Monsoon" . This word is derived from the Arabic word "Mausam" meaning season. The word "monsoon" brings out clearly the seasonal rhythym that prevails causing changes in the direction of winds and the pattern of distribution of rainfall and temperature over the region.

            

            Th e word monsoon is not applied to all cases of seasonal reversal of winds monsoon refers to the more restricted case of seasonal reversal of winds caused by differential heating of land and water surface. This means that monsoon circulation of the daily phenomenon of local wind called land and sea breezes in the coastal region. Monsoon winds are not diurnal winds but seasonal winds caused by several contracts in temperature.

The Origin of the Monsoon

                             It is usual to divide the climatic year of India into four reason:

                              

                              1. Hot weather season (Mid March - Mid May)

                              2. South-West Monsoon season (Mid May - Mid September)

                              3. Reheating Monsoon season (October - Mid December)

                              4. North-East Monsoon season ( Mid December - Mid March)

However, it is the S.W. Monsoon season which dominates the climate of India.

Hot weather Season : The origin of the monsoon can be studied only if one examines the climates of India in the pre-monsoon season, that is, the hot season from the middle of March to middle of May. With the apparent movement of the sun north to the Equator, surface temperature start increasing. In April, most part of the Northern plains including Rajasthan have mean temperature of 38^oC to 43^oC. The temperature increasing still further during may and maximum temperature may exceed 45^oC in most part of the Northern Plains.

In south India, the pre-monsoon showers are called mango shower. Kerala coast, also get rainfall from thunderstorms. These are pre-monsoon shower.

In the plains of northern and north-western India, hot loo winds, blowing dust are common. The hot weather season is generally dry except for occasional shower of local origin.

The Monsoon Season : The monsoon season "burst" during the last week of May over the Andaman and Nicobar Island, strikes the Kerala coast in the first week of June and get established over the whole country by end of June. The surface winds of the monsoon are south-westerly over the west coast and they advance rapidly and reach Mumbai by over 10^th June. The Bay of Bengal branch of the Monsoon is experienced as southerly winds over West Bengal and advances westward up to the Ganga plains. The Arabian sea branch which strikes the west coast is more spectacular than the Bay of Bengal Branch.

Retreating Monsoon : By the beginning of September, temperature begins to decrease. The low pressure trough in the northern plains become less intense. Pressure starts increasing gradually. Monsoon withdraws from Punjab by the middle of September. By the middle of October, Monsoon withdraws completely from north India. Tamil Nadu coast receives bulk of its rainfall in the month of October and November. Monsoon withdraws from the whole of India by the first week of December.

Thus, the monsoon season prevails over the country from June to September and start retreating from September to December. The cold-weather season or winter prevails in the month of December, January and February.

Cold-Weather Season : Mean January temperature varies from 20^oC to 25^oC over the peninsula to 10^oC to 15^oC in northern plains. The low pressure trough of summer monsoon is replaced by a high pressure. Winds are westerly and northwesterly over the northern plains, and northeasterly over the Bay of Bengal. Winds are feeble and variable in direction. Dry condition prevail over most of the country. Westren disturbance give rainfall and snowfall to parts Jammu & Kashmir, Himachal Pradesh, Punjab and Haryana. Tamil Nadu coast also get some rainfall from north-east winds. The Cold weathern season is succeeded by the hot season from March to May.