- The earth is surrounded by a thick layer of air. This thick layer of air is called the atmosphere.
- The thick layer of air that surrounds the earth’s crust is called atmosphere.
- The biosphere of the earth consists of three different spheres, which are: hydrosphere, lithosphere and atmosphere.
- The atmosphere consists of different types of gases like nitrogen, oxygen, carbon dioxide, neon, argon, etc.
- It also consists of water vapour and dust particles.
- The atmosphere covers the lithosphere and hydrosphere of the earth in the form of canopy.
- Therefore, atmosphere is the canopy of air around the earth.
- The air present in the atmosphere keeps on moving due to the effect of the earth’s gravity.
Structure of Atmosphere
- As the altitude increases, the layer of atmosphere becomes thinner, and then temperature also varies at different heights.
- According to the altitude and temperature, the atmosphere is divided into five different layers. They are as follows:
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- It is the lowermost layer of the atmosphere which extends up-to 16 km from the surface of the earth.
- It contains a large amount of heavy gases like nitrogen, oxygen, carbon dioxide, inert gases, water vapour, dust particles, etc.
- Various activities related to the weather like cloud formation, wind, light, rain, hail stone, lightning, fog formation, etc. take place in this layer.
- Therefore, the troposphere is very important for meteorologists.
- Scientists forecast the weather by studying this layer.
- The temperature of the troposphere changes according to the height.
- So, this layer is also called a variable layer.
- There is a fall of about 6.50C in temperature in this layer per kilometer increase in altitude.
- The troposphere is thinner at the poles. About 95% of atmosphere lies in the troposphere.
- The uppermost part of this layer is called the tropopause.
- It separates the troposphere and stratosphere. It has about -560C temperature.
- This layer lies at about 8 to 10 km from the poles and about 16 km from the equator.
- It is the second layer of the atmosphere located between the troposphere and mesosphere.
- This layer extends from 16 km to 50 km vertically upward from the earth’s surface.
- The stratosphere consists of the ozone layer at its upper surface. So it is also called ozonosphere.
- The ozone layer is formed and destroyed at about 20-25km upwards in the presence of solar radiation.
- The ozone absorbs most of the solar radiations and stops it from entering the earth which creates favourable condition for living beings of the earth.
- In the stratosphere the temperature increases from -56oc to -2oc as the height increases.
- The temperature of lower layer of stratosphere is about -53oc .This layer contains thin cloud.
- There is negligible amount of humidity in this layer. The uppermost boundary of this layer is called the stratospause.
- It separates stratosphere and mesosphere.
- It is the third layer of atmosphere located between the stratosphere and thermosphere.
- It extends from out altitude of 50km to 80 km above the earth’s surface.
- The temperature of mesosphere decreases with increase in height.
- The temperature of this layer varies from -2oc to -109oc with increase in height.
- In the mesosphere strong wind blows from west to the east during winter and from the east to the west during spring season.
- The streaks of hot gases released from meteors can be seen in this layer.
- This layer does not determine climate and weather.
- The upper most boundary of mesosphere is called mesopause.
- It separates the mesosphere and thermosphere. The temperature of the mesosphere is about -109oc during summer.
- It is the layer of atmosphere located between the mesosphere and exosphere.
- It extends from 80km to 720km vertically upward from the earth’s surface.
- This sphere occupies about 0.01% of the total region of the atmosphere.
- The lower region of thermosphere contains ions of nitrogen, oxygen etc.
- The gases molecules like nitrogen, oxygen etc. under go ionization and give ions due to the effect of UV radiation of the Sun.
- Therefore, thermosphere is also called the ionosphere. In this layer, there is very high temperature due to the effect of the solar radiation.
- The upper region of the thermosphere mainly contains hydrogen and helium.
- It is the outermost layer of the atmosphere which extends beyond the thermosphere.
- The temperature of this layer is very high i.e. about 1200oc to 6000oc.
- In exosphere, the density of air is very low, but the wind blows at high speed.
- This layer is very far from the earth’s surface so there is no effect of gravity.
- The exosphere mainly contains hydrogen and helium.
- The exosphere forms the outermost edge of the atmosphere. So, it is also called the fringe region.
Atmosphere: Introduction and Structure