Climatology for Kerala PSC: Structure of the Atmosphere
May 28, 2022 2022-05-28 11:00Climatology for Kerala PSC: Structure of the Atmosphere
The structure of the atmosphere is highly complex. The atmosphere consists of different layers with varying densities and temperatures.
● The temperature changes irregularly with height. Density is highest near the surface of the earth and decreases with increasing altitude.
● The column of the atmosphere is divided into five different layers depending upon the temperature condition. They are:
1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere
5. Exosphere.
Troposphere
● The troposphere is the lowermost layer of the atmosphere which immediately overlies the earth’s Surface.
● The air we breathe exists here.
● This layer contains dust particles and water vapour. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.
● The troposphere is the important layer since it is the locale of all the vital atmospheric processes which create the climatic and weather conditions on the earth’s surface.
● The troposphere is the densest part of the atmosphere.
● Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator.
● The thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convection currents.
● The troposphere at any latitude is thicker in summer than in winter.
● The temperature in this layer decreases at the rate of 1°C for every 165m of height. This is called Normal Lapse Rate. This is the most important layer for all biological activity.
● in the lower part of the troposphere, the lapse rate along the vertical is very steep.
● Innumerable vertical currents moving throughout the year cause the troposphere to remain unstable.
● This instability leads to upward movement, condensation, formation of clouds and precipitation.
● The transition separating the troposphere from the stratosphere is termed tropopause.
Stratosphere
● The stratosphere is found above the tropopause and extends up to a height of 50 km.
● One important feature of the stratosphere is that it contains the ozone layer.
● The lower portion of the stratosphere has a maximum concentration of ozone is called Ozonosphere. It is found in between the height of 15 km to 35 km above sea level.
● This layer absorbs ultraviolet radiation and shields life on the earth from intense, harmful forms of energy. Therefore, temperature rises in this layer.
● This layer is free from atmospheric disturbance, making conditions most ideal for flying aero planes.
● This layer is also almost free from clouds and associated weather phenomena.
● The transition separating the stratosphere from the mesosphere is termed stratopause.
Mesosphere
● This is the third layer of the atmosphere.
● The mesosphere lies above the stratosphere, which extends up to a height of 80 km.
● Meteorites burn up in this layer on entering from space.
● In this layer, the temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80 km.
● The upper limit of the mesosphere is known as mesopause.
Thermosphere
● In the thermosphere, the temperature rises very rapidly with increasing height.
● The ionosphere is a part of this layer.
Ionosphere
● The ionosphere is located between 80 and 400 km above the mesopause.
● Since the layer contains electrically charged particles called ions, it is known as the ionosphere.
● Radio waves transmitted from the earth are reflected in the earth by this layer.
● The temperature here starts increasing with height.
(a) D Layer (between the height of 60 km to 90 km): It reflects the signals of low-frequency radio waves but absorbs the signals of medium and high frequency. This layer disappears with the sunset.
(b) E Layer (between the height of 99 km to 130 km): It is also known as the Kennelly-Heaviside layer. This layer reflects the medium and high-frequency radio waves back to Earth.
(c) F layer (at the height of 250 km): It reflects back high-frequency radiowaves. The phenomenon of Aurora generated in this layer is called Aurora Borealis in the North Pole and Aurora Australis in the South Pole.
Exosphere
● The uppermost layer of the atmosphere above the thermosphere is known as the exosphere.
● It extends beyond 640 Km
● The charged particles are concentrated in two bands at about 3,000km and 16000 km above the surface.
● These particles are the result of traping of the cosmic particle by Earth’s Magnetic field and is called the Van Allen radiation belt.
● The particles seen in the layer are extremely rarefied and it gradually merges with outer space.