Climatology for Kerala PSC: Types of Wind

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Kerala PSC

Climatology for Kerala PSC: Types of Wind

  Winds can be broadly divided into three types.

1. Permanent winds

2. Seasonal winds

3. Local winds

Permanent winds

●  The trade winds, westerlies and easterlies are the permanent winds.

●  These blow constantly throughout the year in a particular direction between high pressure belt to low Pressure belts.

Trade winds

●  Winds blowing from the subtropical high pressure belts towards the equatorial low pressure belt are called Trade winds.

●  The word ‘trade’ has been derived from a Latin word, ‘tread’, which means constant direction.

●  The monsoons are also part of the planetary wind system but of a different nature.

●  These trade winds blow from the north-east direction in the northern hemisphere and  from the south-east in the southern hemisphere.

●  The trade winds from both hemispheres converge at the Inter Tropical convergence Zone (ITCZ).

●  Trade winds have contrasting properties in different parts.

●  In their areas of origin, they are descending and stable. Hence the poleward parts are dry.

●  As the trade wind approaches the equator, they become more humid and warmer and their instability produces copious rainfall.

Westerlies

●  The Westerlies are the winds blowing from the subtropical high-pressure belts towards the subpolar low-pressure belts.

●  They blow from the south west in the northern hemisphere and from the north- west in the southern hemisphere.

●  The poleward boundary of the westerlies is highly fluctuating and there are many seasonal and short fluctuations.

●  Westerlies carry much west to east moving temperate cyclones with them.

●  Roaring forties, furious fifties and shrieking sixties are dreaded terms for navigators.

Polar Easterlies

●  The Polar Easterlies or Polar winds blow from the polar high pressure to the subpolar low-pressure areas. In the northern hemisphere, their direction is from the north-east.

●  In the southern hemisphere they blow from the south-east.

Seasonal winds

●  These winds change their direction in different seasons.

●  The pattern of wind circulation is modified in different seasons due to the shifting of regions of maximum heating, pressure and wind belts.

●  The most pronounced effect of such a shift is noticed in the monsoons, especially over southeast Asia.

The Monsoon

●      The surface winds which change their directions with changing seasons in Indian Ocean are called monsoon winds.

●      These winds blow from sea to land in summer and from land to sea in winter. This is because of differential heating of land and water.

●      These winds originate in the belt of trade winds lying between the Tropic of Cancer and the Tropic of Capricorn. These winds are common in South and South-East Asia.

Local winds

●  These blow only during a particular period of the day or year in a small area.

●  Differences in the heating and cooling of earth surfaces and the cycles that develop daily or annually can create several common, local or regional winds.

Land and Sea Breezes

●  The land and sea absorb and transfer heat differently.

●  During the day the land heats up faster and becomes warmer than the sea. Therefore, a low pressure is created over the land and a relatively high pressure over sea. 

●  Thus, pressure gradient from sea to land is created and the wind blows from the sea to the land as the sea breeze.

●  In the night the reversal of conduction takes place. The land loses heat faster and is cooler than the sea.

●  The pressure gradient is from the land to the sea and hence land breeze results

Mountain and Valley Winds

●  In mountainous regions, during the day the slopes get heated up and as a result the air moves upslope and to fill the resulting gap. The flow of air from the valley blows up the valley is known as the valley breeze.

●  During the night the slopes get cooled and the dense air descends into the valley as the mountain wind.

Katabatic wind

●  The cool air of the high plateaus and ice fields draining into the valley is called katabatic wind.

●  Another type of warm wind occurs on the leeward side of the mountain ranges. The moisture in these winds, while crossing the mountain ranges condense and precipitate.

●  When it descends down the leeward side of the slope the dry air gets warmed up by an adiabatic process. This dry air may melt the snow in a short time.

Foeh or Chinook

●  It is the most well-known hot wind in the middle latitude.

●  It occurs on the lee side of a mountain range and causes extremely rapid evaporation of snow or soil moisture.

●  The warm and moist air ascends the slope and causes rainfall.

●  The wind helps in removing snow from grazing ground and also the early ripening of the grapes.

Simoom

●  It is a hot, dry, suffocating wind or whirlwind which blows during the spring and the summer in the Sahara and Arabian desert.

●  It carries dense masses of sand thereby reducing the visibility.

Mistral

●  This cold wind flows in the winter from higher land and snow-capped mountains to the north onto the Mediterranean Coast of France

●  It is a dry wind with high velocity.

Karaburan

●  It is the hot north-easterly wind experienced in the Tarim Basin of Sinkiang.

●  The sand blown by the Karaburan cause major changes in the course of desert rivers

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