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Atmospheric pressure and Layers

Layers of atmosphere    The atmosphere is divided into four layers based on the variations in temperature and composition different regions ...

Layers of atmosphere  

The atmosphere is divided into four layers based on the variations in temperature and composition different regions at different altitudes from the surface of the earth.

1.Troposphere:- The layer of atmosphere which is in contact with the earth's surface is called troposphere.  The range of temperature in this layer is close to that of the earth since it is just above this layer, the temperature decreases with increase in altitude up about -50 ° C.  It lies between 0 km and 10 km above the earth's surface and contains the maximum percentage of the total mass of the atmosphere. 

 2.Stratosphere:-The layer of atmosphere above the troposphere is called stratosphere.  In this layer temperature range does not alter up to a height of about 25 km above this, the temperature gradually decreases up to a range of 0 ° C - 10 ° C.  It lies between 10 km and 50 km above the surface of the earth.

3.Mesosphere:- The layer succeeding the stratosphere is called mesosphere.  In this layer, the range of temperature is lower than that of the layers below it.  It lies between 50 km and 80 km above the surface of the earth.  

4.Thermosphere:- This is the topmost layer of atmosphere and it is called so due the very high temperatures prevailing there.  The basic reason for this is that the atmosphere in this layer absorbs intense solar radiation.

 The composition of air is not uniform throughout the atmosphere.  It varies from one layer to the other layer.

Atmospheric pressure 

The atmosphere in any layer is composed of air, which exerts a downward pressure, and this downward pressure exerted by air due to its weight on the surroundings is called Atmospheric pressure.   

 Since pressure is defined as the force exerted per unit area, it is expressed in Newtons / metre2  which is called Pascal.  Hence, the SI unit of pressure is pascal (Pa) or kilopascal. 

Measurement of the atmospheric pressure 

Since the composition and the density of air vary with the altitude, the pressure exerted by air also Waries.  The atmospheric pressure decreases with an increase in the altitude.  It is due to this reason that the atmospheric pressure is measured at sea level where it is maximum. 
 The instrument used to measure the atmospheric pressure is called barometer.  Two types of barometers are in use for this purpose .

 1.Aneroid barometer 

2.Mercury barometer