what are pressure belts? describe the pressure belt of the earth
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Pressure belts are seasonally identical horizontal pressure variations created in the earth’s atmosphere just above the earth’s surface due to seasonal and spatial variation of energy received by the earth at different places. [Energy received determines the pressure exerted by the atmosphere at a place and variations in pressure exerted determines the direction and velocity of the wind.]
(i) Equatorial Low Pressure Belts
This low pressure belt extends from 0 to 5° North and South of Equator. Due to the vertical rays of the sun here, there is intense heating. The air therefore, expands and rises as convection current causing a low pressure to develop here. This low pressure belt is also called as doldrums, because it is a zone of total calm without any breeze.
(ii) Subtropical High Pressure Belts
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. So the winds from subtropical region blow towards Equator as Trade winds and another wind blows towards Sub-Polar Low-Pressure as Westerlies.
(iii) Circum-Polar Low Pressure Belts
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. This zone is marked by ascent of warm Subtropical air over cold polar air blowing from poles. Due to earth’s rotation, the winds surrounding the Polar region blow towards the Equator. Centrifugal forces operating in this region create the low pressure belt appropriately called Circumpolar Low Pressure Belt. This region is marked by violent storms in winter.
(iv) Polar High Pressure Areas
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. These areas of Polar high pressure are known as the Polar Highs. These regions are characterised by permanent Ice Caps.
SHIFTING OF PRESSURE BELTS
If the earth had not been inclined towards the sun, the pressure belts, as described above, would have been as they are. But it is not so, because the earth is inclined 23 1/2° towards the sun. On account of this inclination, differences in heating of the continents, oceans and pressure conditions in January and July vary greatly. January represents winter season and July, summer season in the Northern Hemisphere. Opposite conditions prevail in the Southern Hemisphere. When the sun is overhead on the Tropic of Cancer (21 June) the pressure belts shift 5° northward and when it shines vertically overhead on Tropic of Capricorn (22 December), they shift 5° southward from their original position. The shifting of the pressure belts cause seasonal changes in the climate, especially between latitudes 30° and 40° in both hemispheres. In this region the Mediterranean type of climate is experienced because of shifting of permanent belts southwards and northwards with the overhead position of the sun. During winters Westerlies prevail and cause rain. During summers dry Trade Winds blow offshore and are unable to give rainfall in these regions. When the sun shines vertically over the Equator on 21st March and 23rd September (the Equinoxes), the pressure belts remain balanced in both the hemispheres.
hope it helps you a lot.
thank you very much
(i) Equatorial Low Pressure Belts
This low pressure belt extends from 0 to 5° North and South of Equator. Due to the vertical rays of the sun here, there is intense heating. The air therefore, expands and rises as convection current causing a low pressure to develop here. This low pressure belt is also called as doldrums, because it is a zone of total calm without any breeze.
(ii) Subtropical High Pressure Belts
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. So the winds from subtropical region blow towards Equator as Trade winds and another wind blows towards Sub-Polar Low-Pressure as Westerlies.
(iii) Circum-Polar Low Pressure Belts
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. This zone is marked by ascent of warm Subtropical air over cold polar air blowing from poles. Due to earth’s rotation, the winds surrounding the Polar region blow towards the Equator. Centrifugal forces operating in this region create the low pressure belt appropriately called Circumpolar Low Pressure Belt. This region is marked by violent storms in winter.
(iv) Polar High Pressure Areas
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. These areas of Polar high pressure are known as the Polar Highs. These regions are characterised by permanent Ice Caps.
SHIFTING OF PRESSURE BELTS
If the earth had not been inclined towards the sun, the pressure belts, as described above, would have been as they are. But it is not so, because the earth is inclined 23 1/2° towards the sun. On account of this inclination, differences in heating of the continents, oceans and pressure conditions in January and July vary greatly. January represents winter season and July, summer season in the Northern Hemisphere. Opposite conditions prevail in the Southern Hemisphere. When the sun is overhead on the Tropic of Cancer (21 June) the pressure belts shift 5° northward and when it shines vertically overhead on Tropic of Capricorn (22 December), they shift 5° southward from their original position. The shifting of the pressure belts cause seasonal changes in the climate, especially between latitudes 30° and 40° in both hemispheres. In this region the Mediterranean type of climate is experienced because of shifting of permanent belts southwards and northwards with the overhead position of the sun. During winters Westerlies prevail and cause rain. During summers dry Trade Winds blow offshore and are unable to give rainfall in these regions. When the sun shines vertically over the Equator on 21st March and 23rd September (the Equinoxes), the pressure belts remain balanced in both the hemispheres.
hope it helps you a lot.
thank you very much
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Answer:
Clearly identifiable and homogenous horizontal zones of pressure, across the earth’s atmosphere are known as ‘pressure belts’.
Explanation:
Pressure belts are created as a result of expansion and contraction of air when it gets heated or cooled. Temperature variations therefore, cause difference in air pressure. Air flows from high pressure areas to low pressure areas.
There are seven distinct pressure belts in the earth’s atmosphere. They are the Equatorial low-pressure belt also known as Doldrums, the Sub-Tropical high-pressure belts in both hemispheres, the Sub-Polar low-pressure belts in both hemispheres and the Polar high-pressure belts in both hemispheres.
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