Stratification

On the basis of the variation in air temperature. the atmosphere has been divided vertically into four layers: (figure shown below) thee troposphere, stratospG, mesosphere and thermosphere.

Troposphere or the lowermost layer extends up to an altitude of 15 km at the equator to 8 km at the poles. The temperature in this zone decreases with increasing altitude or height.

The next layer, the stratosphere, extends up to an altitude of approximately 50 km. Here a gradual increase in temperature occurs with altitude. Pilots of jet aircraft prefer to fly in the stratosphere as it is relatively stable and free from weather fluctuations apart from providing excellent visibility. Scientists are womed about the growing pollution in the stratosphere. As pollutants enter into this zone, they are likely to remain here for a long time. We shall be elaborating this later.

In mesosphere, the next layer, temperature is constant in the lower portion but then rapidly decreases with altitude. At 80 km the temperature is the lowest in the atmosphere (average -90" C). Above this is the thermosphere in which the temperature again increases at higher altitudes. Human activity at present seems to have little direct impact on the outermost atmospheric layer.