The atmosphere is a thick blanket of air that surrounds the earth. The atmosphere provides us with oxygen to breathe as well as protects us from harmful radiation from the sun. Composition of atmosphere:
- Nitrogen 78 %
- Oxygen 21 %
- Argon 0.9%
- Other gases (Carbon dioxide, nitrous oxide, methane, ozone) 1%
Structure of the Atmosphere:
There are five main layers of the atmosphere:
It extends to a height of 8 km from the poles and 18 km from the equator. It is the lowest layer of the atmosphere where all weather-related phenomena take place. The upper layer of the troposphere is called tropopause.
It is the second-lowest layer of the earth and extends from the upper layer (tropopause) up to 50km. There is no weather up there and this is the zone that consists of the ozone layer. The stratosphere is otherwise known as Ozonosphere. The lower layer of the stratosphere is where the aeroplanes fly.
This layer extends after the stratosphere from 50km to 80km. It is located in between the stratosphere and the thermosphere. On reaching the mesosphere, the temperature decreases because of the increase in altitude.
This layer of atmosphere extends between 80-400 km and it is suitable for radio waves transmission. Radio waves are transmitted from this layer and reflected the earth.
It is the topmost and thinnest layer of the atmosphere. Hydrogen and helium gas floats in this layer.
Air is all around us. It’s a mixture of different gases. The air in Earth’s atmosphere is made up of approximately 78 per cent nitrogen and 21 per cent oxygen. Our atmosphere is divided into five layers starting from the earth’s surface. The five layers are Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. Weather is this hour-to-hour, day-to-day condition of the atmosphere. The average weather condition of a place for a longer period represents the climate of a place.
It is the pressure exerted by the weight of wind on the surface of the earth. The pressure of the air decreases with height. The pressure of air is highest at sea level and the lowest in the mountains. Air pressure is divided into two types i.e., anticyclone (when the air pressure is high) or cyclone (when the air pressure is low). The pressure of air is measured by a barometer. Following are the main pressure belts found around the globe are:
1. Equatorial Low-Pressure Belt (doldrums):
The air at the equator receives a high amount of heat throughout the year thus the heated air is light which creates a low-pressure belt at the equator. The low-pressure belt is located on either side of the equator in a zone extending between 5o N and 5o S. Due to low pressure and its calm condition, this belt is known as a belt of calm’ or doldrums.
2. Sub-tropical High-Pressure Belt:
The high-pressure belt zone is also known as horse latitude. It is located 25o-35o in both hemispheres. At this pressure belt as the earth rotates the air at the equator moves towards the poles which results in the cooling and sinking of air towards the 30o N and 30o S.
3. Sub Polar Low-Pressure Belt:
This belt is located at 60O – 65O latitudes in both hemispheres. At this belt in the subtropical region, the air gets divided into two parts. One part blows the equatorial low-pressure belt and the other blows from the circumpolar low-pressure belt. In this region, warm air blows from subtropics over cold air from the poles. So, due to the rotation of the earth low pressure is produced.
4. Polar high-pressure belt:
This belt is situated between 70o and 90o on both poles. At this belt, the temperature is very low and thus creates very high pressure on both poles.
This belt is situated at the equator at 5o N and 5o S at this belt the temperature is very high which creates low pressure also here two trade wind meets and this zone is known as the Inter-Tropical Convergence Zone (ITCZ).
2. Trade Wind Belt (Hadley):
These winds extend from 5 to 30 latitudes on either side of the equatorial trough of a low-pressure area.
3. Prevailing westerlies:
This belt is situated 30 N to 60 S on both hemispheres. When these winds move on higher latitudes they are diverted and become southwesterly and northwesterly.
4. Polar easterlies:
These winds are the dry cold wind that blows around the polar regions. These winds move out of the polar high towards the subpolar low-pressure belt.
Cyclones and Anticyclones:
A cyclone is a system of wind that rotates at the centre of the low atmospheric pressure belt anticlockwise in the north of the equator and clockwise in the south of the equator.
It is a system of high atmospheric pressure where winds rotate clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. Anticyclones are formed due to the cooling of air masses and then their surrounding which makes the air heavy and dense. These dense airs create high pressure in the area. These may occur without any precipitation so the winds remain dry in anticyclones.
|Serial No.||Book Name||Author Name|
|1.||CTET Success Master Social Science/Studies Paper-2||Arihant Experts|
|2.||General Knowledge 2022||Manohar Pandey|
|3.||General Knowledge||Arihant Experts|
|4.||Lucent's General Knowledge|
R. P. Suman, Vinay Karna, Sanjeev Kumar, Renu Sinha, Manvendra Mukul
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