tropopause

thumb|right|300px|The tropopause extends to high altitudes in the tropical latitudes and extends to low altitudes in the polar latitudes. The tropopause is the atmospheric boundary that demarcates the lowest two layers of the atmosphere of Earth – the troposphere and stratosphere – which occurs approximately above the equatorial regions, and approximately above the polar regions.

==Definition== thumb|The atmosphere of planet Earth: The tropopause is between the troposphere and the stratosphere. Rising from the planetary surface of the Earth, the tropopause is the atmospheric level where the air ceases to become cool with increased altitude and becomes dry, devoid of water vapor. The tropopause is the boundary that demarcates the troposphere below from the stratosphere above, and is part of the atmosphere where there occurs an abrupt change in the environmental lapse rate (ELR) of temperature, from a positive rate (of decrease) in the troposphere to a negative rate in the stratosphere. The tropopause is defined as the lowest level at which the lapse rate decreases to 2°C/km or less, provided that the average lapse-rate, between that level and all other higher levels within 2.0 km does not exceed 2°C/km. The tropopause is a first-order discontinuity surface, in which temperature as a function of height varies continuously through the atmosphere, while the temperature gradient has a discontinuity.