PTR SCIENCE
The movement of air from high pressure area to low pressure area is called wind. Wind always blow from high pressure to low pressure areas. Winds transfer tropical heat towards the poles and the polar coldness toward the topics. So in this way, winds act as a means for transfer of heat from one part of the earth to another. They are deflected towards the right in Northern hemisphere and towards the left in the southern Hemisphere.
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Any change in the atmospheric pressure change the speed and strength of the Wind.
There are mainly four types of winds
• Permanent winds or Planetary winds
• Periodic winds
• Local winds
• katabatic winds
★ Permanent winds
winds which blow throughout the year in a particulate directions are called permanent winds. They originate due to the presence of high and low pressure belts on the surface of the earth. They are of the following types:---
(1) Trade Winds: Trade winds blow from the sub-tropical high pressure belts to the equatorial low pressure belt in both the hemispheres. This winds follow the Ferrel's Law which states that all the moving bodies on the surface of the earth deflect towards their right in the Northern hemisphere and towards their left in the southern hemisphere.
(2) Easterlies winds: It is a prevailing Wind blowing from the East. The trade winds in tropical region and the prevailing wind in the polar regions are Easterlies.
(3) Westerlies winds: Winds blow from the sub-tropical high pressure belts to the sub-polar low pressure belt in both the hemispheres is generally in West direction. They are also known as anti-trade winds as they blow opposite to the direction of the trade winds.
★ Periodic winds
Apart from the regular winds, there are many other seasonal winds which blow during a particular season. The an equal heating and cooling of the Earth's surface causes this winds to blows. Monsoon winds and sea and land breeze are the example of this kind of winds. The monsoon winds blow in the topics. They are rain-bearing winds that are of vital importance to the areas over which they blow. They change their direction once in every 6 months.
Anabatic winds: these winds are upslope wind driven by warmer surface temperatures on a mountain slope than the surrounding air column.
Land breezes: On clear, calm evenings, temperature differences between a body of water and Neighbouring land produced a cool wind that blows offshore. This wind is called a "land breeze" land breezes are strongest along the immediate coastal line but we can considerably further inland. At night, the land cool down the sea. The air over the sea is now warmer and lighter. The warm air over the sea rises creating low pressure. Now, since the pressure over the sea is lower than the pressure on land, the air from the land starts blowing towords the sea.
Sea breeze: The sea-Breeze is a circulation that develops due to differential heating of air over land and sea. As the sun hits the boundary layer over land, the resulting pressure gradient causes the moment of low-level air from the sea to land (sea-Breeze) with a return flow Aloft (return current).
During the daytime, the land gets heated up faster than the sea. As a result, high pressure prevails over the sea and low pressure over the land. Thus, the wind blows from the sea to the land.
★ Local winds
Local winds blow over a limited area for a short time. They are mostly seasonal and have local Significance. They have different names in different regions. Some local wind are:---
The loo is a hot, dry and dusty wind that blows during the summer months. It originates from the desert of Rajasthan and carries the dust and sand of the desert to the alluvial plains of the Ganga.
Chinook means the 'snow-eater'. This one and dry wind helps to clear the snow and ice rapidly after winter. Ek blouse down the eastern side of the rockies.
'Foehn' is a general term for any worm, strong and dry local wind that is quite similar to Chinook and blouse down the southern parts of the Alps during winters. In Southern Europe, this wind helps to ripening of the grapes.
Harmattan is a dry and dusty wind that blows over North-West Africa. It's blows between the end of November and the middle of March. It carries the sands of the Sahara to North America even. As the wind carries tiny sand particles, it troubles a lot although it provides relief from damp heat of the tropics.
★ Katabatic winds
Winds which blow from the high elevations of mountain, plateaus and hills down the slope to the valleys and plains below are not as katabatic winds.
★ Measuring winds
The direction and speed of the wind or never fixed. The vertical movement of air is called air current.
A wind vane is used to find the direction of the Wind.
Wind speed is measured with the help of an instrument called the the anemometer.
