Atmosphere - Wind Pattern of the world (Civil Services Preparation Online)

Atmosphere – Wind Pattern of the world

by Devender

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The pattern of winds differs at different places due to various reasons and climate conditions. Let's take a complete look at the pattern of wind around the world.

Atmosphere – Wind Pattern of the world

  • Planetary Winds:
  • These winds are also known as permanent or prevailing winds. These blow throughout the year in a particular direction from high to low pressure over the earth's surface and oceans. These winds are divided into 3 categories namely: Trade Winds (Tropical Easterlies), Westerlies, and Polar winds (Polar Easterlies).

  • Trade Winds (Tropical Easterlies):
  • These winds blow from subtropical high-pressure areas to equatorial low-pressure areas and are extremely steady. These winds have a tendency to hold moisture as they become dry and hot upon travelling from high latitude to low latitude areas.

    These winds also cause considerable rainfall on the eastern margins of the continents after blowing over oceans and gathering moisture. After that, these winds converge near the equator and form ITCZ causing heavy rainfall by rising and are absent in the north Indian ocean which is dominated by Monsoon winds.

  • Westerlies:
  • These winds blow from subtropical high-pressure belts towards subtropical low-pressure belts and blow from SouthWest to NorthEast under Coriolis effect in the Northern Hemisphere & from NorthWest to SouthEast in the Southern Hemisphere from low to high latitudes.

    These winds cause rainfall particularly on the western margins of the continents and are more consistent in direction. These winds blow with a very strong force in the southern hemisphere due to the absence of too many obstructions from continents. They are also known as brave winds or roaring forties, furious fifties & shrieking sixties.

    Note:

    Because of the earth's inclination which causes shifting of wind belts, not all the western coast of the temperate zone (30 – 60 Degree) receive Westerlies throughout the year.

    When the sun is over the tropic of cancer in June, all the belts move about 5–10 Degree north of their average position. Hence, Mediterranean parts of continents that come under the effect of westerlies receive rainfall in June and vice versa in December when the Sun is overhead tropic of Capricorn.

  • Polar Winds:
  • These wind blows from polar high to the subpolar low-pressure belt and is very cold in nature as they come from polar areas. These winds don't cause much rainfall but when they come into contact with westerlies, they result in cyclones and brings frequent changes in weather conditions causing heavy rainfall.


  • Shifting of Wind belts:
  • The wind belts keep on shifting northward or southward, it totally depends on the movement of the sun. On March 21 & Sept 23 known as Equinoxes, the sun shines vertically over the equator and the equatorial low-pressure belt lies between 5 Degree North - 5 Degree South. After 21 March, the sun starts shifting towards the North, and hence, the whole system of pressure belts moves northward.

    On June 21, the Sun shines vertically over the Tropic of cancer, and hence, all the pressure belts move 5 – 10 Degree northward from the original position.

    On December 21, the Sun shines vertically over the Tropic of Capricorn, and hence, all the pressure belts move 5 – 10 Degree southward from the original position. So, the shift in world pressure belts also causes a shift in the world’s wind system.


  • Periodic/Seasonal winds:
  • These are the winds that change their direction periodically such as Monsoon Winds, Land & Sea Breeze, Mountain and Valley Breeze.

  • Monsoon Winds:
  • These winds are those which reverse their direction completely with the change of seasons. Halley’s law suggests that blow from sea to land during summers and land to sea during winters, due to differential in heating of continents and oceans.

    During the summer season, the sun shines vertically over the Tropic of cancer which results in high temp. and low pressure in central Asia whereas the pressure remains high at the Bay of Bengal and the Arabian Sea. This brings the flow of wind from Sea to land bringing heavy rainfall in India and its neighboring countries.

    During the winter season, the sun shines vertically over tropic of Capricorn so, India becomes colder than the Bay of Bengal and Arabian sea which results in reversal of the monsoon. The theory of differential heating was replaced by shifting of ITCZ for monsoon in India & neighboring countries.

  • Land & Sea Breeze:
  • These winds can only affect a narrow strip of 20 – 30 km along the coast. When the sun shines, it blows from sea to land which is called Sea breeze. While at night, it blows from land to sea which is called Land breeze.

  • Mountain & Valley Breeze:

During the daytime, the slopes of the Mountain get heated more than the valley, and hence, the air from the valley blows upward which is called the Valley breeze whereas, after the sunset, the pattern changes, and hence, air flows from mountains to valley which is known as Mountain Breeze.



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