Pressure Belts of Earth: Shifting, Types, Sub Tropical High Pressure Belt

By K Balaji|Updated : October 21st, 2022

The pressure belts of the Earth are a series of layers of atmospheric pressure areas that encase the planet, forming high and low air pressure spectrums. There are seven pressure belts existing on the Earth’s surface, which are Equatorial Low, the two Subpolar lows, the two Subtropical highs, and the two Polar highs. The tropical regions are thought to be one big area. The subtropical high-pressure belt, which exists on the subtropical area, is considered the first among the pressure belts. These regions are directly linked to the distribution and recurrence of tropical cyclones.

The study of climate, weather patterns and geography is significantly influenced by global pressure belts. It is a crucial component of UPSC GS 2. In the UPSC exam, questions about the pressure belts of Earth, its types and factors responsible for their shift have regularly been asked.

Table of Content

What are Pressure Belts?

Pressure belts are regions on the surface of the Earth occupied by high or low-pressure cells. These belts of pressure are not meant to be there indefinitely. They tend to shift through time with the noticeable movement of the sun. They fly south in the winter and north around the summer in the northern hemisphere. Seasonal climatic perturbations end up causing shifts in pressure belts, particularly between latitudes of around 30° and 40° in both hemispheres.

Factors affecting Pressure Belts of Earth

The pressure differences that lead to high and low-pressure systems on the surface of Earth, hence affecting global pressure belts, are driven by two primary factors: thermal and dynamic.

Pressure Belts PDF

Thermal Factors:

Air, whenever heated, expands and thus loses density. This results in lowering pressure. Cooling, on the other hand, causes contraction. This raises the density and, as a result, the pressure. Thermal lows, as well as thermal highs, are both formed by the development of equatorial lows and polar highs, respectively.

Dynamic Factors:

Aside from temperature variations, the formation of pressure belts can be understood by the rising of dynamic controls from pressure gradient forces and the earth's rotation (which is known as the Coriolis force).

Distribution of Pressure Belts of Earth

The pressure belts of Earth are distributed on two bases- there is vertical distribution of pressure belts and horizontal distribution of pressure belts. Both these types of pressure belts are discussed in detail in the section below:

Vertical Distribution of Pressure Belts of Earth

The vertical distribution of pressure refers to the columnar distribution of pressure in the atmosphere.

  • As a result of the volume of air present above in the column of air pushing down the air beneath it, the basal layer of the atmosphere is denser than the upper layers; due to this, there is higher density in the lower layers in the atmosphere and thus, exerting more pressure.
  • The pressure of air over a particular time and place is affected by the temperature of the air, the volume of vapours of water that exists in the air, and also the gravitational force exerted by the earth.
  • Because these variables are controlled with altitude, the air pressure reduction rate varies with altitude.
  • Falling pressure implies unsteady and cloudy weather, while rising pressure suggests settled and fine weather.
  • The higher layers, on the other hand, are less tightly packed and thus have lower density and pressure.

Horizontal Distribution of Pressure Belts of Earth

There are multiple factors that tend to affect the horizontal distribution of pressure belts on Earth’s surface. The following factors lead to the variations in the horizontal distribution of pressure:

Air temperature:

Because of the disparities in insolation, differential heating and cooling of water and land surfaces, the Earth does not get warmed up uniformly. Air pressure is lesser in the regions close to the equator and highest in the regions close to the poles. Reduced air pressure in equatorial regions is caused by hot air ascending up there with a progressive reduction in temperature, resulting in thin air over the surface. On the other hand, cold air is quite dense in polar regions, so it goes down, and the pressure rises.

The Earth’s rotation:

The rotation of the earth produces centrifugal force. This causes air to be deflected from its original location, resulting in a decrease in pressure. The earth's rotation leads to the formation of low-pressure belts in the subpolar regions and, simultaneously, the formation of high-pressure belts in the subtropical regions.

Presence of water vapour:

Air with a higher concentration of water vapour tends to have lower pressure, while air with a lower concentration of water vapour exerts higher pressure.

Types of Pressure Belts on Earth’s surface

There are a total of seven pressure belts on the earth’s surface. These are:

  • Equatorial Low
  • The two Subtropical Highs
  • The two Subpolar Lows
  • The two Polar Highs

All these seven pressure belts are discussed in detail in the section below:

Equatorial Low Pressure Belts

This low-pressure zone stretches from 0 to 5 degrees to the north and south of the Equator. The vertical sun rays cause intense heating persists. As a result of the convection current, the air rises and expands, resulting in low pressure to occur here. This equatorial low-pressure belt is also known as the doldrums since it is completely calm with no breeze.

Subtropical High Pressure Belts

The ascending air currents from the equator descend around 30° North and also the South of the Equator. As a result, this is a high-pressure zone. The Horse's latitude is another name given for it. Wind, thus, always blows from high to low pressure.

Sub Polar Low Pressure Belts

Circumpolar Low-Pressure Belts or Sub polar Low Pressure Belts are those that are positioned between 60° and 70° in every hemisphere. The sliding air is split into two parts in the Subtropical region. One section of the wind blows towards the direction of the Equatorial low pressure Belt. The other portion of the wind shifts towards the Sub polar Low Pressure Belts.

The rise of warm subtropical air on top of the cold polar air gusting from the poles defines this zone. Because of the rotation of the Earth, the winds that surround the Polar region gust towards the Equatorial region.

Polar High Pressure Areas

Temperatures at the North and South Poles, which are usually between 70° and 90° north and south, are indeed exceptionally low. The cold air descending downwards causes high pressures to build up over the Poles. The Polar Highs are these areas of Polar high pressure which are distinguished by permanent Icecaps.

Pressure Belts UPSC

The pressure belts on the earth’s surface are an important segment of the General studies UPSC syllabus. In order to fully understand the pressure belts on the earth’s surface, it is crucial to be well-versed in the climatic factors and varied geographical patterns. You should also consume the UPSC study material offered on a daily basis.

Following is a sample multiple choice question that will provide you with an idea of the type of questions that will appear in the examination about Pressure belts UPSC topic:

Question: Which of the following statements holds true for the Vertical Distribution of Pressure Belts of Earth?

  1. the volume of air present above in the column of air pushing down the air beneath it, the basal layer of the atmosphere is denser than the upper layers;
  2. there is higher density in the lower layers in the atmosphere and thus, exerting more pressure.
  3. Because these variables are controlled with altitude, the air pressure reduction rate varies with altitude.

Choose the appropriate response from the given following options:

  1. 1 only
  2. 2 only
  3. 1 and 2 only
  4. 1, 2 and 3 only

Answer: (D)

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FAQs on Pressure Belts

  • There are a total of seven pressure belts on the earth’s surface. These are as follows:

    • Equatorial Low
    • The two Subtropical Highs
    • The two Subpolar Lows
    • The two Polar Highs
  • The pressure created by a load of air on the surface of the Earth is known as air pressure. The pressure drops quickly as we ascend the atmospheric layers. The pressure of air is greatest at sea level and declines with altitude. The air temperature at a particular location influences the horizontal distribution of air pressure. Where the temperature is particularly high, the air heats up and rises. This results in the formation of a low-pressure zone. The air is cooler and heavy in areas with lower temperatures. Heavy air tends to sink, resulting in a high-pressure zone on the Earth's surface.

  • When heated, air expands and loses density. As a result, the pressure drops. This is how the thermal factors affect the pressure belts of Earth. Conversely, cooling causes contraction. This increases density and, as a result, pressure. Thermal lows and highs are created by the development of equatorial lows and polar highs, respectively.

  • This low-pressure area extends from 0 to 5 degrees north and south of the Equator. The vertical sun rays continue to cause intense heating. The air rises and expands as a result of the convection current, resulting in low pressure here. Because there is no breeze, this equatorial low-pressure belt is also known as the doldrums.

  • The following are the factors that affect the Horizontal Distribution of Pressure Belts of Earth:

    • Air temperature
    • The Earth’s rotation
    • Presence of water vapour
  • The shifting of the pressure belts tends to happen with time because of the noticeable movement of the sun. When the sun is shining vertically above the Tropic of Cancer (21 June), the belts of pressure shift 5° northward and 5° southward whenever the sun shines upright on the Tropic of Capricorn (22 December).

    Seasonal climatic variations are triggered by the movement of pressure belts, particularly between 30° and 40° latitudes across both hemispheres. This zone has a Mediterranean climate due to the shifting of permanent belts towards the south and the north with the sun's position overhead.

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