Prepare notes on the role of solar energy and the Earth's rotation in the formation of pressure belts.

Pressure belt is seasonally identical horizontal pressure variations created in the earth's atmosphere due to the seasonal and spatial variation of energy received by the earth at different places. In the formation of pressure belt, solar energy and Earth’s rotation played a different role. Let us understand the following:

a. Equatorial low-pressure belt: This is the zone where the sun's ray’s fall vertically throughout the year therefore temperature will be high in this zone. This low-pressure belt extends from 0 to 5° North and South of Equator. As the air expands due to the sun's heat and rises up on a massive scale. The air, therefore, expands and rises as convection current causing low pressure to develop here. This pressure belt is also known as 'doldrums', meaning 'the zone with no winds'. This low-pressure belt is also called as doldrums because it is a zone of total calm without any breeze.

b. Subtropical high-pressure belt: The hot air ascending from the equatorial low-pressure belt cools gradually and subsides at the subtropical zone due to the rotation of the Earth. At about 30°North and South of Equator lies the area where the ascending equatorial air currents descend. This area is thus an area of high pressure. It is also called as the Horse latitude. Winds always blow from high pressure to low pressure.

c. Subpolar low-pressure belt: As this zone is close to the Pole, the air is colder here. Though the cold air remains close to the Earth, the air is thrown away due to the rotation of the earth. As a result, low pressure is experienced all along the subpolar region. These belts located between 60° and 70° in each hemisphere are known as Circum-Polar Low-Pressure Belts. In the Subtropical region, the descending air gets divided into two parts. One part blows towards the Equatorial Low-Pressure Belt. The other part blows towards the Circum- Polar Low-Pressure Belt. Due to earth’s rotation, the winds surrounding the Polar region blow towards the Equator.

d. Polar high-pressure belt: This zone experiences severe cold throughout the year. As a result, the air remains chilled under the extreme cold that prevails over the Poles, and this contributes to the steady high pressure experienced here. At the North and South Poles, between 70° to 90° North and South, the temperatures are always extremely low. The cold descending air gives rise to high pressures over the Poles.

This shows how variations in the amount of solar energy received and the rotation of the earth contribute to the formation of different pressure belts.