Tropopause

The tropopause is the upper boundary of the troposphere , a layer of the earth's atmosphere near the ground. In the troposphere, the temperature generally decreases with increasing altitude, with restricted exceptions called inversions. However, at a height of about 6 mi (10 km) at the poles 9 mi (15 km) at the equator, the temperature abruptly becomes constant with increasing altitude. This isothermal region is called the stratosphere , and the interface between it and the troposphere is called the tropopause. Mixing of air across the tropopause is slow, occurring on a time scale of weeks on the average, while tropospheric mixing is more rapid.

The existence of the stratosphere is largely caused by the absorption of solar energy , mostly ultraviolet light, by oxygen to form ozone . The balance of the heating is caused by absorption of other parts of the solar spectrum by other trace gases.

See also Ultraviolet radiation

tropopause The boundary separating a lower layer of the atmosphere (troposphere), in which air temperature generally decreases with height, from the layer above (stratosphere), in which temperature remains constant or increases with height. The altitude of the tropopause varies according to sea-surface temperature and season, but also over shorter periods, from an average of 10–12 km over the poles (occasionally descending to 8 km or below) to 17 km over the equator. See also ATMOSPHERIC STRUCTURE.

tropopause The boundary separating a lower layer of the atmosphere (troposphere), in which air temperature generally decreases with height, from the layer above (stratosphere), in which temperature remains constant or increases with height. The altitude of the tropopause varies according to sea-surface temperature and season, but also over shorter periods, from an average of 10–12 km over the poles (occasionally descending to 8 km or below) to 17 km over the equator.