General weather system of India

Weather & Climate

    Climate refer to the sum total of weather condition and variation over large area for a longer period of time. Weather refers to the state of the atmosphere over an area at any point of time.

The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity and precipitation. On the basis of the generalized monthly atmospheric conditions year is divided into seasons.

    India situated in the northern hemisphere; the tropic of cancer passes through the middle part of the country. As a result the southern half of the country has a tropical climate. 

During the winter season in the Northern hemisphere, Northern half of the country is warmer than the areas of similar Latitude about 3° to 8° Celsius. This is due the fact that the Himalayas check the cold polar air mass entering into India. In other countries like USA the polar air mass invade as much as 20° N latitude. 

    The Northern part of the country does not have the mid-day sun almost vertically overhead, and the southern part of the country have sun overhead twice in a year. 

    The southern part of the country is influenced by the sea. The southern tropical climate zone of the India is warmer then the northern and does not have a clear-cut winter season. 

    The climate of India is described as the monsoon type, which means perceptible reversal of the wind system. The Arabs, came to India as traders, named this seasonal reversal of the wind system as monsoon.  

    The monsoon is influenced by (i) Latitude (ii) Nearness to the sea (iii) Altitude (iv) Direction of prevailing wind (v) Direction of mountain ranges etc., 

    The monsoons are experienced in the tropical area roughly between 20°N and 20°S. To understand the mechanism of the monsoons, the following facts are important.

How monsoon forms? 

(a) The differential heating and cooling of land and water creates low pressure on the landmass of India while the seas around experience comparatively high pressure.

(b) The shift of the position of Inter Tropical Convergence Zone (ITCZ) in summer, over the Ganga plain (this is the equatorial trough normally positioned about 5'N of the equator).

(c) The presence of the high-pressure area, east of Madagascar, approximately at 20oS over the Indian Ocean. The intensity and position of this high-pressure area affects the Indian Monsoon

(d) The Tibetan plateau gets intensely heated during summer which results in strong vertical air current over the plateau at about 4 km above sea level.

(e) The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer.

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Reference:

1. Atmosphere, Ocean, and Climate Dynamics - An Introductory Text (John Marshall & R. Alan Plumb).

2. Climatology – second edition – (John E Oliver, John J Hidore)

3. Atmospheric Thermodynamics - John M. Wallace, Peter V. Hobbs.