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atmospheric pressure and wind - Coggle Diagram
atmospheric pressure and wind
Factors affecting wind-
a.Tempreature
When air gets heated, it expands and becomes light and rises vertically. Rising warm air exerts very little pressure on the surface, thus causing a low pressure. Similarly, when air is cooled it becomes heavy and sinks vertically and exerts greater pressure on the surface, thus creating high pressure.
Altitude
The upper atmosphere is very thin and less dense than the lower atmosphere. the pressure is also less and keeps decreasing with increasing altitude or height.
Pressers belts-
Equatorial Low Pressure
(This belt extends 5°N and 5°S of the equator. Being in the Torrid Zone, the area receives the maximum heat of the sun and, therefore, air rises vertically, creating a low pressure. This belt is nicknamed 'doldrums' because no surface movement of winds takes place in this belt
Sub-tropical High Pressure Belt
These are located beyond the tropics around 30°N and 30°S latitudes. The air that rises from the equatorial belt cools and sinks down in this belt creating a belt of high pressure. This belt is also known as the 'horse latitudes'. This is also a belt with no surface movement of winds.
Sub-polar Low Pressure Belts
The belt is located around 60°N and 60°S latitudes. This is a zone where very cold winds from the polar areas meet with the warm winds blowing from the tropical regions.
Polar High Pressure Belts
The poles are zones of intense cold throughout the year and, therefore, remain areas of high pressure.
Atmospheric pressure is measured in millibars with the help of an instrument called barometer.
Air has weight
Movement of air from high-presser area to low presser area is called wind.
PLANETARY WINDS
Air in motion is called wind. On the surface of the earth, winds blow from high pressure to
low pressure These are the planetary winds. These are also called permanent winds as they blow all round the year. They do not blow straight but are deflected from their path due to the rotation of the earth. The rotation of the earth creates the Coriolis effect, which causes the deflection of winds from their direct path of flow. The Coriolis effect is explained in Ferrel's law, which states that wind and water get deflected to the right in the northern hemisphere and to the left in the southern hemisphere.
There are three permanent winds on the surface of the earth: Trade Winds, Westerlies and Polar Winds.
Westerlies
These winds blow from sub-tropical high pressure belts to the sub-polar low pressure belts. They blow from the south-west in the northern hemisphere and from the north-west in the southern hemisphere. As they blow from a relatively warmer region to a cooler region, they cause plenty of rain to the western coast of the continents.
PERIODIC WINDS
The periodic winds are also called seasonal winds since they blow only during a particular season. The unequal heating and cooling of land and water is the main cause of these winds-land gets heated faster than water and thus becomes an area of high temperature and low pressure.
LOCAL WIND
Local winds blow in specific areas and last for a short duration. In different parts of the world these are known by different names.
Loo
These are hot and dry local winds that originate from the Thar Desert of Rajasthan during the hot summer months and blow across the Ganga Plain. These winds raise the temperature considerably.
Chinook
These are local winds that blow down the eastern slopes of the Rocky Mountains in USA. As these winds sink down, they warm the region and help in melting the winter snow and ice. Chinook means the 'snow eater'.
