Environmental Science 3(3+0)

(4) Thermosphere

• Above the mesosphere is the thermosphere which extends upto 500 km above the earth’s surface and is characterized by steady temperature increase with height from mesopause. The thermosphere includes the region in which UV radiation and cosmic rays cause ionization of molecules like oxygen and nitric oxide. This region is called the ionosphere. In the thermosphere molecules of air so widely spaced that high frequency audible sounds are not carried by the atmosphere.