Atmosphere is the transparent envelope of gases surrounding the earth. It is formed of several layers varying in temperature, density, composition and properties. Density of atmosphere is maximum near the earth’s surface and decreases with altitude.

Up to 10 km from sea level, temperature decreases with increasing height. So, temperature in the lowlands/backwaters region is higher than in the mountains 2-3 km above sea level, as in Thekkady, Munnar, etc.