tropopause

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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.

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