The stratosphere is the so-called second "floor" of the earth's atmosphere. It extends after the tropopause in about 12 km altitude to a height of about 50 km and closes there with the Stratopause.
Characteristics of the stratosphere
In the stratosphere, the temperature increases on average with increasing altitude, although this gradient in the lower stratosphere, up to about 20 kilometers, is still negligible. This temperature increase with altitude distinguishes the stratosphere from the layers of air surrounding it. This inverse temperature profile is mainly caused by the ozone in the stratosphere, which absorbs UV radiation from the sunlight and converts radiant energy into heat.
As a result, a significant portion of the UV light is prevented from penetrating to the earth's surface. The heat is strongest in the area of the ozone layer, where the temperature rises from approx. -60 ° C to just below 0 ° C.
The exchange of air between the troposphere and the stratosphere is very small because the vertical temperature differences are so great. The cold air of the troposphere is significantly heavier than the warmer air of the stratosphere above it, so that vertical movements of air are quickly slowed down.
An exception are the resulting tropopausal folds resulting from low pressure areas, which can lead to a better mixing of the air. Since the upper troposphere is so cold, there may be little water vapor there, so the air is dry (in absolute terms). If this air enters the stratosphere, it becomes warmer and the relative humidity is extremely low - the air can potentially absorb more water, but there are no sources of water. For this reason, the stratospheric air is very dry and clouds usually form in the stratosphere only in the extremely cold conditions of the polar night. Such so-called mother-of-pearl clouds contain acids and produce a dazzling light due to uniform crystal structures.
Original-Source:
http://wiki.bildungsserver.de/klimawandel/index.php/Stratosph%C3%A4re
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