stratosphere (strat'-o-sphere). The layer of the atmosphere extending from 10 km to 50 km, overlying the troposphere; characterized by a region of constant temperature for the first several km. Between 20 km and 50 km the temperature increases with altitude, reaching a temperature maximum at the stratopause (approximately 50 km). The temperature of the stratosphere results from the absorption of ultraviolet radiation by the oxygen and ozone molecules between 30 km and 50 km.