Pressure Belts of the Earth

Our earth is not flat, instead, it is spherical, and due to this reason, some regions are heat surplus and some are heat deficit. This change in temperature at many places developed different pressure systems all over the globe, and further, these pressure systems give rise to wind systems as well, but for now, let us understand more about the different pressure belts of the earth.

What are Pressure Belts?

The regions on the surface of the earth experience the same pressure depending upon different latitudes. High or low-pressure cells cause the formation of high or low-pressure belts.

Earth is divided into four large pressure belts. In reality, belts are not continuous as shown below, but are different and exits in packets of low pressure and high pressure.

Pressure Belts and Wind Systems

Warm air, due to its lower density, ascends, creating calm conditions. The absence of significant horizontal wind movement characterizes this tranquility, termed as the ‘doldrums.’ The convergence of winds from the high-pressure belts in both hemispheres forms a region known as the Inter Tropical Convergence Zone (ITCZ). Cool air is heavier and hence, it subsides. Subsidence of air in the tropics causes to additional air accumulation. Therefore, high pressure belt is created here.

Formation of Pressure Belts of the Earth

Let us understand how pressure is created on earth. This is due to THERMAL and DYNAMIC reasons as follows:

1. THERMAL REASONS
2. DYNAMIC REASONS

THERMAL REASONS

As discussed earlier, high temperature cause low pressure and low temperature causes high pressure, Hence, due to variation in temperature, pressure difference is created in various parts of earth.

DYNAMIC REASONS

Pressure can also be created due to convection(vertical movement of air). When air rises, it creates a low pressure below and high pressure upwards. Similarly, when air moves down, it creates a low pressure above it and low pressure below it.

Types Of Pressure Belts

There are mainly 7 pressure belts that exist on planet earth as follows :

• Equatorial Low Pressure Belt
• Sub-Tropical High Pressure Belts (Both in North and South)
• Sub-Polar Low Pressure Belts (Both in North and South)
• Polar High Pressure Belts (Both in North and South)

Equatorial Low Pressure Belt

As, equatorial region is subjected to constant insolation, air in this region gets heated up and rises upwards in the air, creating a low pressure zone in this area. This convectional movement of air gives rises to clouds in the sky (cumulonimbus clouds) and rainfall.

Equatorial Low Pressure Belt is also known as “Belt of calm” because this region is quite calm throughout the year.

Sub-Tropical High Pressure Belts (Both in North and South)

Dynamically induced High pressure developed in this region , air above the equator moves to poles but descends at 30-40 degree latitudes due to Coriolis force. Their energy becomes low and settles down creating a high pressure belt here.

Sub-Tropical High Pressure Belt are also known as “Horse latitudes”.

Sub-Polar Low Pressure Belts (Both in North and South)

From poles, cold wind moves towards equator, both warm and cold winds from Sub-Tropical High Pressure Belts rise up hence a low pressure zone is created on 50-60 degree latitudes in both hemispheres.

Polar High Pressure Belts (Both in North and South)

Air risen at Sub-Polar Low Pressure Belts, descends at poles. Thus a region of High Pressure is created. This pressure, we can say, is thermally induced in this area.

How are these Pressure Belts Induced?

Pressure Belts of Earth	Induced Pressure Type
Equatorial Low Pressure Belt	Pressure is thermally induced.
Sub-Tropical High Pressure Belts (Both in North and South)	Pressure is dynamically induced.
Sub-Polar Low Pressure Belts (Both in North and South)	Pressure is dynamically induced.
Polar High Pressure Belts (Both in North and South)	Pressure is thermally induced.

Summary

Pressure Belts are the regions of same pressure throughout the latitude. Pressure belts, in reality, not as distinct as explained. This is just a theoretical representation for better understanding. The pressure system depends on various atmospheric conditions. Wind systems depends on high and low pressure systems on earth. There are 5 pressure belts namely, Equatorial Low Pressure Belt, Sub-Tropical High Pressure Belts (N and S), Sub-Polar Low Pressure Belts (N and S), Polar High Pressure Belts (N and S), which are either thermally or dynamically induced.

FAQs on Pressure Belts of the Earth

What gives rise to pressure systems on earth?

Heat deficit and heat surplus regions formed on earth because earth is tilted on it’s axis, gives rise to high pressure and low pressure systems.

How wind systems are formed dur to pressure belts ?

As we know that wind movement is from a high pressure zone to a low pressure zone, hence alternative high and low pressure belts thus creates wind system on earth.

Why pressure decreases as height increases ?

Firstly, due to gravity, the gravitational pull decreases as we move away from the surface so pressure decreases. Secondly, because the height of the air column decreases as height increases. In other words, when we are at surface, maximum height of air column is above us exerting pressure, as we move upwards, air column height decreases hence pressure decreases.

How many Pressure Cells are formed due to these pressure belts ?

There are 6 pressure cells which are formed ( 3 in one hemisphere ) namely, Hadley cell (between Equatorial Low Pressure Belt and Sub-Tropical High Pressure Belts ), Ferrel cell (between Sub-Tropical High Pressure Belts and Sub-Polar Low Pressure Belts) and Polar cell (between Sub-Polar Low Pressure Belts and Polar High Pressure Belts)