Tropopause

Tropical Tropopause

Typically, the tropopause height decreases with latitude, being around 3.7 mi. (6 km.) near the poles and 11 mi. (18 km.) near the equator. Whereas radiative and convective processes with time scale of the order of one week to one month basically determine the properties of the tropical tropopause, in the midlati-tudes a relevant role is played also by baroclinic-fuelled extra-tropical cyclones, having a typical time scale of a few days, in such a way that the tropopause readjusts its height in such a way as to act effectively as a stabilizing mechanism limiting the growth of the weather perturbations. The tropopause is not a hard boundary: exchanges of tropospheric and stratospheric air occur through various mechanisms, including vigorous thunderstorms and midlatitude perturbations.

The globally averaged tropopause height tends to increase if the troposphere warms up and/or the stratosphere cools down, and the height change is approximately proportional to the difference between the tropospheric and stratospheric temperature changes. Therefore, the mean tropopause height can act as a robust indicator of climate change. Recent climate simulations have shown that the estimated increase after 1979 of about 492 ft. (150 m.) may be primarily explained by anthropogenic causes, namely the stratospheric cooling driven by ozone depletion and the tropospheric warming driven by increases in the greenhouse gases concentration. Considering natural processes, episodic, short-lived strong reductions of the globally averaged mean tropopause height are caused by large explosive volcanic eruptions, which warm the troposphere and cool the stratosphere.