Climate of India

Climate of India

Introduction
1. climate of a country includes temperature, rainfall, atmospheric pressure & direction & velocity of winds over a long period of time
2. in the north Indian sub-continent is separated from rest of asia by the Himalayan ranges
  1. so cold air masses from central Asia cannot enter India
3. so whole of India South of Himalayas treated as a tropical country
  1. although its norther part is situated in temperate belt
4. the Arabian sea & Bay of Bengal in the south of Indian coast give it a typical tropical monsoon climate
Diversity in the Unity of Indian Monsoon climate
1. the climate of India has many regional variations expressed in
  1. winds, temperature, rainfall, rhythm of seasons & degree of wetness or dryness
2. these climatic differences are due to
  1. location
  2. altitude
  3. distance from sea
  4. relief
Factors Influencing the climate of India
1. influenced by largely geographical factors
2. Location & Longitudinal Extent
3. Distance from the Sea
  1. coasts experience equable climate
  2. interiors experience extreme continental climate
4. The Northern Mountain ranges
  1. Himalayas act as a climatic divide between Indian Sub continent & central Asia
5. Physiography
  1. physical map of India is closely related to climatic conditions of the country
6. Monsoon Winds
  1. most dominating factor of Indian Climate - so called Monsoon climate
7. Upper Air Circulation - Jet Streams
  1. Westerly Jet Stream
  2. Easterly Jet Stream
8. Tropical Cyclones & Western Disturbances
9. El-Nino Effect
10. La Nina
11. Southern Oscillation
The Monsoon Winds
1. Mechanism of the Monsoons
  1. Classical Theory
    1. summer monsoon
    2. winter monsoon
    3. Halley - explained the monsoon as resulting from thermal contrasts between continents & oceans due to their differential heating
  2. Modern Theories
    1. Air mass theory
      1. due to the seasonal shift of ITCZ
      2. Flohn's model
    2. Jet Stream Theory
      1. the Periodic movements of the jet stream are often indicators of the onset & subsequent withdrawal of the monsoon
      2. In winter the western jet stream flows along the southern slopes of the Himalayas but in summer it shifts northwards, rather dramatically, & flows along the northern edge of the Tibet plateau
      3. Yin model
      4. the burst of monsoon depends upon the upper air circulation
      5. the intensity & duration of heating of tibet plateau has a direct bearing on the amount of rainfall in India by the monsoons
      6. when the summer temperature of air over tibet remains high for a sufficiently long time, it helps in strengthening the easterly jet & results in heavy rainfall in India.
    3. Besides differential heating, the development of monsoon is influenced by the shape of the continents, topography, the condition of upper air circulation etc.
    4. Meteorological Teleconnections
      1. Southern Oscillations
        Sea-saw pattern of meteorological changes observed between Pacific & Indian Oceans
        the pattern of low & high pressures over Indian & Pacific oceans give rise to vertical circulation along the equator - Walker Circulation
        low pressure over Indian Ocean in winter months - good for monsoon
        shifting east wards from its normal position in ElNino Years reduces monsoon rainfall in India
        due to close association b/w ElNino & SO - jointly referred as ENSO event
        Southern oscillation index SOI is used to measure the intensity of SO
        this is the difference in pressure between Tahiti representing Pacific ocean & port Darwin in northern Australia representing pacific ocean
        Positive SOI - HP over east pacific Tahiti & Low Pressure over Indian ocean - low rainfall over eastern pacific & good monsoon rain over India & Indian ocean
        HP in Indian Ocean & LP over East pacific - poor monsoon over India & higher then usual rain over east pacific
      2. El Nino
        narrow warm current, which appears off the coast of Peru in dec.
        The Child Christ
        influence Indian monsoon
        when surface temp goes up in southern pacific ocean - India receives deficient rainfall & conversely
2. term monsoon derived from the Arabic Mausam meaning season
3. seasonal winds which reverses their direction of flow with the change of season
4. they flow from sea to land during the summers & from land to sea during winters
5. called as double system of seasonal winds - the sum of summer & winter winds
Seasonal Rhythm
1. The cold Weather season or Winter Season
  1. from NOV to MAR
  2. clear sky, pleasant weather, low temperature & humidity etc.
  3. Temperature
  4. Pressure & winds
  5. Western disturbances & Tropical Cyclones
    1. the spell of fine weather is often broken due to inflow of depressions from the west
    2. the low pressure depressions are called western disturbances
      1. they originate in the Mediterranean sea & enter India
    3. intensify over NW India & reach upto Arunachal Pradesh
      1. lowers temperatures by 5 - 10 degree C
    4. jet streams play important role in bringing these
  6. season of least tropical cyclone activity - due to low sea surface temp & location of ITCZ farthest south
3. The Summer Season
  1. March - June - High temp & low humidity
  2. Pre-monsoon period
  3. temperature
    1. the diurnal range of temp is very high
    2. the temp are lower in southern parts due to moderating effect of the sea
    3. the temp of west coast are comparatively lower than those prevailing on the east coast due to prevailing westerly winds
    4. Northern & central part experience heat waves i.e. 6-8° more than normal - because of their location far away from the sea.
    5. the strong north westerly winds check the onward sea breeze over eastern coastal belt & create heat wave conditions over coastal A.P & Orissa
  4. Pressure & Winds
    1. Low pressure - high temp
    2. during may june - high temp in NW India builds - hot, dust laden & strong wind known as loo blows
    3. strong dust storms - Andhis - thunderstorms from NW bring small showers - give relief from scorching heat
    4. the strong westerly winds or western disturbances in upper troposphere lead to thunderstorms in east & north-eastern part of the country - they normally originate over chota nagpur plateau & carried eastwards by westerly winds - known as Norwesters - some times hailstones - cause heavy damage to crops - mainly occur during mid March - Mid April - of Vaisakh month - locally known as Kalabaisakhis - black storms
    5. western disturbances still prevails with their frequency & intensity gradually decreasing - these cause change in weather conditions, bringing cloudiness & convective activity
    6. few tropical cyclones originate in Bay of Bengal & Arabian sea
  5. Precipitation
    1. 1% of annual rainfall receive during this season
    2. Norwesters bring rainfall of about 50 cm in NE India - also known as spring storm showers
    3. there will be some mango showers in A.P & T.N

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	Created by dheerudheerajk about 8 years ago