Study Notes on EARTH'S ATMOSPHERE (Part 2)

Structure of the Atmosphere

The atmosphere consists of almost concentric layers of air with varying density and temperature.

a) Troposphere:

• Lowest layer of the atmosphere  

• The height of troposphere is 16 km thick

over the equator and 10 km thick at the poles.

• All weather phenomena are confined to troposphere (e.g. fog, cloud, frost, rainfall, storms, etc.)

• Temperature decreases with height in this layer roughly at the rate of 6.5° per 1000 metres, which is called normal lapse rate.

• Upper limit of the troposphere is called tropopause which is about 1.5 km.

b) Stratosphere:

• The stratosphere is more or less devoid of major weather phenomenon but there is

circulation of feeble winds and cirrus cloud in the lower stratosphere.

• Jet aircrafts fly through the lower stratosphere because it provides conducive flying conditions.

• Ozone layer lies within the stratosphere mostly at the altitude of 15 to 35 km above

earth's surface.

• Ozone layer acts as a protective cover as it absorbs ultra-voilet rays of solar

radiation.

• Depletion of ozone may result in rise of temperature of ground surface and lower

atmosphere.

• Temperature rises from -60°C at the base of the stratosphere to its upper boundary

as it absorbs ultra-voilet rays.

• Upper limit of the Stratosphere is called stratopause.

c) Mesosphere

• Mesosphere extends to the height of 50- 90 km.

• Temperature decreases with height. It reaches a minimum of -80°C at an altitude

of 80-90 km

• The upper limit is called mesopause.

d) Thermosphere

• It lies at 80 km to 640 km above the earth's surface.

• It is also known as ionosphere.

• Temperature increases rapidly with increasing height.

• It is an electrically charged layer. This layer is produced due to interaction of solar radiation and the chemicals present, thus disappears with the sunset.

• There are a number of layers in thermosphere e.g. D-layer, E-layer, Flayer and G-layer.

• Radio waves transmitted from earth are reflected back to the earth by these layers.

e) Exosphere

• This is the uppermost layer of the atmosphere extending beyond the ionosphere.

• The density is very low and temperature becomes 5568°C.

• This layer merges with the outer space.

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