14.2 Layers of Atmosphere

Atmosphere consists of four spheres (layers) extending from the surface of the Earth upwards. The concentration of the component gases decreases gradually upwards, that results in gradual decrease of pressure. But temperature of the atmosphere does not change in a gradual way. It varies in a complex way as shown in figure 14.1.

Depending upon the temperature variation, atmosphere is divided into four regions.

Temperature decreases from $17^{\circ}C$ to $- 58^{\circ}C$ regularly in the lowest layer extending upto $12km$ . This layer of atmosphere is called troposphere. Above this layer lies the stratosphere that extends upto $50km$ . In this layer, temperature rises upto $2^{\circ}C$ . Beyond the stratosphere lies the mesosphere, covering upto $85km$ . In this region, again temperature decreases down to $- 93^{\circ}C$ . Beyond $85km$ lies the thermosphere, in which temperature goes on increasing upwards.

We will discuss the reasons of variations of temperature and other phenomenon in troposphere and stratosphere in detail.