ICSE Class 9 Answered

The four major pressure belts of the Earth are:

1. Equatorial Low Pressure Belt
• This belt lies between 0⁰ to 5⁰N and 0⁰ to 5⁰S.
• Since the vertical rays of the Sun fall on the Earth, the heat is intense and the temperature is high. The air becomes warm and expands.
• The convection currents help to spread the heat to the upper layers of the atmosphere also.
• This leads to the creation of a low pressure belt in the region. Winds in this pressure belt do not blow at a fast pace and hence this belt is also known as the Belt of Calms or the Belt of Doldrums.
2. Sub tropical High Pressure Belt
• This belt is located between 30⁰N to 35⁰N and 30⁰S to 35⁰S.
• As the air at the Equator moves towards the Poles, it begins to cool and sink down at about 30⁰ North and South of the Equator. This creates areas of high air pressure.
• Due to the rotation of the Earth, air from 60⁰N and 60⁰S also descends in the Sub tropical Belts.
• This pressure belt is also a Belt of Calms and is referred to as the Horse Latitudes.
3. Circum-polar Low Pressure Belt
• This belt is located between 60⁰N to 65⁰N and 60⁰S to 65⁰S.
• It is a zone of two winds; the warm Westerly winds meet the cold polar Easterlies.  As the Westerlies are lighter, they rise over the cold polar winds creating low pressure area.
• These belts experience stormy weather and cyclonic activity especially during the winters.
4. Polar High Pressure Belts
• This belt is located between 85⁰N to 90⁰ N and 85⁰S to 90⁰S.
• The Polar regions experience cold climatic conditions as the rays of the Sun are extremely slanting.
• The cold air sinks down giving rise to high pressure areas.
• In places where the temperature is permanently low, the air is dense and heavy. These Polar regions have permanent ice caps.