Atmosphere Composition, Composition, Major Layers and Main Gases
What is the atmosphere called?
The gaseous cover of the air that surrounds the earth is called the atmosphere. The atmosphere is a mixture of many gases. In addition to the atmosphere, the Earth's lithosphere is made up of solid materials and the hydrosphere is made up of water. The lowest layer of the atmosphere is the troposphere. The part above it is called the stratosphere and the part above it is called the ionosphere. The part between the troposphere and the stratosphere is called the "calmosphere" and the space between the stratosphere and the ionosphere is called the stratopause. Generally the upper floors remain very quiet. The height of the atmosphere is said to be from 16 to 29 thousand km, but only 800 km above the surface, the atmosphere is more important.
Main gases of the atmosphere:
The atmosphere is a mixture of many gases. Following are the names of the main gases present in the atmosphere:
|Name of gas||Percentage by volume|
Layers of the Atmosphere:
The density of the atmosphere decreases with altitude. The atmosphere is divided into 5 different layers.
- It is closest to the surface of the earth. Its height decreases from the equator (16 km) towards the poles (8 km). All weather events take place in this layer.
- It is denser than all other layers and contains water vapor, dust particles, moisture etc. The troposphere is responsible for most of the weather related changes.
- The temperature in this layer decreases with height. For every 165 metres, there is a decrease of 1°C in temperature. This is called the normal temperature loss rate.
- The rate of decline is not only affected by altitude but also by latitude. According to this law, this rate is high above the surface of high temperature and low above the surface of low temperature.
- The troposphere boundary at the top of the troposphere separates it from the stratosphere. It is also called the convection circle.
- Its height is up to 50 km.
- The temperature in the stratosphere does not increase with altitude. The temperature remains the same.
- This layer is ideal for pilots.
- The upper boundary of the stratosphere is called the stratopause.
- Water-vapor, dust particles etc. are not found in this circle. It lacks clouds.
- Ozone gas is found in abundance in the lower part of this mantle. This ozone-dominated zone is called the ozone zone.
- The ozone layer is present in this layer, which absorbs the ultraviolet rays of the sun and does not allow them to reach the surface and protects the earth from overheating.
- It occurs up to an altitude of 80 km.
- In this there is a drop in temperature with altitude and 80 km. At altitudes, the temperature rises to -100°C.
- It is also called thermosphere.
- The spread of this circle is 50 km. from 400 kms. up to the height of .
- The temperature in this circle increases rapidly.
- The radio waves transmitted from the earth collide in this circle and return back to the earth.
5. Outer Circle:
- It is the topmost layer of the atmosphere.
- The temperature at its outer limit is about 5568 °C.
- Hydrogen and helium gases predominate in it.
What is atmospheric pressure called?
The weight of all the layers of the atmosphere above on the surface or on the sea level per unit of area is called air pressure. It is measured by barometer. Air pressure is maximum at sea level. As the amount of water vapor in the atmosphere increases, the air pressure decreases. Areas of low pressure have less atmospheric mass over those locations, while areas of higher pressure have more atmospheric mass over those locations. Similarly, the atmospheric mass above that level decreases as altitude increases, so the pressure decreases with increasing altitude.
Air pressure belts:
1. Equatorial low pressure belt
- It extends from 0° latitude to 5° latitude in both the hemispheres.
- Here maximum insolation is received, so the air becomes lighter and rises above it. This creates a low pressure here.
- The air in this region is almost motionless or calm. That's why it is also called calm zone.
- The Earth's rotational velocity is highest at the equator.
2. Sub-tropical high pressure belt
- Its extent is from 30° to 35° latitudes in both the hemispheres. Despite the high temperature, high air pressure remains here, the reason for this is the daily motion of the earth and the differential and divergence in the air.
- Winds continuously rise from the equator and collect here as well as winds from the subpolar low pressure belt also collect. Because of this the air pressure is high here.
- This belt is also called Horse Latitude because the sailors of ancient times had a lot of difficulty due to the high pressure in this area. So they had to throw some horses into the sea to lighten the load of the ships.
3. Subpolar low pressure belt
- It extends from 60° to 65° latitudes in both the hemispheres.
- Here the pressure is low even though the temperature is low because due to the rotational motion of the earth, the air from here spreads outwards, hence the air pressure decreases.
- Another reason for this is the presence of extremely high pressure at the poles.
4. Polar High Pressure Belt
- Due to extreme cold, high pressure is found at both the poles.
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