The atmosphere which surrounds our Earth is a thousands of kilometers thick coat made of many gases. This gaseous cover exerts pressure on the land, which is called air pressure.
Air pressure belts: In determining the belts of air pressure found in the world, there is also the role of rotating motion of the earth along with the relation between temperature and pressure.
On this basis, there are two types of air pressure belts:
1. Thermally Induced Belt.
2. Dynamic Induced Belt.
The description of all these belts is given as follows:
1. Equatorial low pressure belt: The expanse of this belt extends from 5° north to 5° south latitudes on both sides of the equator. Due to the sun rays falling directly all over the year, the temperature is always high and the air pressure is low. There is excess of water vapor in the atmosphere and the density of the air is low. The speed of rotation on the equator is the highest, due to which, the centrifugal force is the highest here.
Surface horizontal winds do not blow in this belt, but because of high temperature, the air lightens and rises upwards, and the convection currents are born. Therefore, this belt is also called the equatorial ‘belt of calm’ or ‘Doldrum Belt’. This is a Thermally Induced Belt.
2. Sub – tropical High Pressure Belt: These belts are located between the 30° to 35 0 latitude on both sides of the equator. High temperature, high air pressure and cloudless sky are found throughout the year. One of the main features of this belt is that all the hot deserts of the world are located in this belt on the western edges of the continents.
Due to the absence of friction in the upper part of the atmosphere, these winds in the northern and southern hemispheres turn towards their right and left respectively. These high air pressure regions are also called ‘Horse Latitudes’. This is a Dynamic Induced Belt.
3. Sub – polar Low Pressure Belt: This belt is located between 60° to 65° north and south latitudes. Low temperature is found in these latitudes. But here, lower air pressure is found instead of high pressure. The reason for this is the rotational speed of the earth. As hot streams flow in this region temperature is found to be more due to which air pressure is less. This is also a Dynamic Induced Belt.
4. Polar high pressure belt: Due to low temperature near the poles, there is always high pressure. Both of these belts located in the two hemispheres are heat generated. The temperature of the poles and their adjoining areas remains low throughout the year so their surface part always remains glaciated. Therefore, the air near the surface, is very cold and heavy. For this reason, the surface pressure data can not be obtained in sufficient detail from here.
