the plane of discontinuity between the troposphere and the stratosphere, characterized by a sharp change in the lapse rate and varying in altitude from about 18 km (11 miles) above the equator to 6 km (4 miles) at the Poles
tropopause in American English
(ˈtroʊpəˌpɔz; ˈtrɑpəˌpɔz)
noun
an atmospheric transition zone or shell located between the troposphere and the stratosphere at an altitude of c. 10 to 20 km (c. 6 to 12 mi), in which temperatures and atmospheric stability begin to increase with increasing altitude