Pressure belts are the natural phenomenon for which different types of air pressure on the earth’s surface can be experienced in different zones of the earth. The air pressure is completely dependent on the temperature and the height.
Distribution of Pressure
- The columnar distribution of atmospheric pressure is known as vertical distribution of pressure.
- Air pressure decreases with increase in altitude but it does not always decrease at the same rate.
- Dense components of atmosphere are found in its lowest parts near the mean sea level.
- Temperature of the air, amount of water vapour present in the air and gravitational pull of the earth determine the air pressure of a given place and at a given time.
- In high mountainous areas rice takes more time to cook because low pressure reduces the boiling point of water.
- Breathing problem such as faintness and nose bleedings are also faced by many trekkers from outside in such areas because of low pressure conditions in which the air is thin and it has low amount of oxygen content.
(b) Horizontal Distribution
- The horizontal distribution of atmospheric pressure is not uniform in the world. It varies from time to time at a given place; it varies from place to place over short distances.
- The factors responsible for variation in the horizontal distribution of pressure are as follows:
- (i) Air temperature
- (ii) The earth’s rotation
- (iii) Presence of water vapour
Equatorial Low-Pressure Belts
- From 0 to 5 degrees north and south of the Equator, this low-pressure belt exists.
- There is a lot of heat here because of the sun’s vertical rays.
- As a result of the convection current, the air expands and rises, causing low pressure to occur here.
- Because it is a zone of complete quiet with no breeze, this low-pressure belt is also known as the doldrums.
Subtropical High-Pressure Belts
- The location where the ascending equatorial air currents drop is located around 30° North and South of the Equator.
- As a result, this is a high-pressure zone.
- The Horse latitude is another name for it.
- Winds are continually blowing from high to low pressure.
- As a result, trade winds blow from the subtropical zone towards the Equator.
Circum Polar Low-Pressure Belts
- Circum-Polar Low-Pressure Belts are belts that run between 60° and 70° in each hemisphere.
- The descending air in the Subtropical zone is split into two portions.
- One part of the wind is directed toward the Equatorial Low-Pressure Belt.
- The remaining half of the wind is directed towards the Circumpolar Low-Pressure Belt.
- The rise of warm Subtropical air above frigid polar air moving from the poles defines this zone.
- The winds that encircle the Polar area blow towards the Equator due to the earth’s rotation.
- The Circumpolar Low-Pressure Belt is a low-pressure belt created by centrifugal forces occurring in this region.
- During the winter, this area is known for its strong storms.
Polar High-Pressure Areas
- Temperatures are always exceptionally low between 70° and 90° North and South at the North and South Poles.
- High pressures from above the Poles due to the chilly descending air.
- The Polar Highs are these areas of high pressure in the Arctic.
- Permanent IceCaps describe these locations.
Shifting of Pressure belts
- This system of pressure belts is a generalised picture.
- In reality, the location of these pressure belts is not permanent.
- They shift northward in July and southward in January, following the changing position of the sun’s direct rays as they migrate between the Tropics of Cancer and Capricorn.
- The thermal equator (commonly known as the belt of highest temperature) also shifts northwards and southwards of the equator.
- With the shifting of thermal equator northwards in summer and southwards in winter, there is also a slight shift in pressure belts towards north and south of their annual average location.
Significance of Pressure Belts
- The seasonal changes in the climate are caused by the shifting of these pressure belts.
- The movement of these belts results in rainy winters and dry summers, as the region is influenced by moisture-laden westerlies in the winter and dry trade winds in the summer.
- As a result, rainfall is evenly spread throughout the year, despite the fact that it is rather low due to continental impact.
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