Dry Adiabiatic Lapse Rate The inflection point at 50km is called the stratopause, anthe stratopause, and the region above this is the mesosphere. This is often called the "ignorosphere" because it is so difficult to get detailed measurements from here, though a sustained effort in recent years is now beginning to pay off. There are no in-situ heat sources in the mesosphere of note but it loses heat by emission from CO 2 , O 3 and (higher up) NO, so it is a cold region, and drops in temperature to the mesopause at about 85 km which is the coldest place on Earth. Curiously it is coldest in summer due to the counter-intuitive circulation pattern here. There are a number of theories to explain this (ranging from chemical effects to adiabatic cooling of ascending air driven by large-scale horizontal circulation). The mesopause acts as a sink for the heat generated in the thermosphere above it. The thermosphere is heated mainly by absorption of EUV and XUV radiation. Up to 105 km the
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