Atmospheric physics 10: Temperature anomaly

Water vapor occurs in the atmosphere only within the troposphere in significant quantities, so that clouds occur only at altitudes up to 15 kilometers. The condensation of water vapor into fine water droplets therefore takes place almost exclusively in the troposphere and therefore can not contribute to increasing the temperature in the stratosphere and mesosphere.

Atmospheric circulation also occurs exclusively in the troposphere. The reason is the positive temperature gradient in the stratosphere, which causes a very stable air stratification, so that no up and down wind is possible. Only violent volcanic eruptions can move particles from the earth's surface into the stratosphere.

In the lower and middle atmosphere ( $z < 100 \,\text{km}$ ), there is only a low ion concentration, so that there is no question of a plasma state. However, the high atmosphere ( $z > 100 \,\text{km}$ ) is ionized to a high degree by short-wave solar radiation. This atmosphere layer is therefore electrically conductive and can reflect radio waves, which can be used in broadcasting to increase the transmitter range.

Part of the short-wave solar radiation, the ultraviolet radiation, penetrates into the stratosphere and troposphere. In the stratosphere, however, a large part of the UV spectrum is absorbed by the so-called ozone layer. The ozone ( $\text{O}_3$ ) is produced by the photolytic cleavage of atmospheric oxygen and reaches concentrations in the stratosphere of up to 8 ppm (parts per million). Despite the low concentration, the ozone absorbs most of the UV radiation through the ozone-oxygen cycle via the following reactions $\begin{aligned} \text{O}_3 + \text{UV radiation} &\rightarrow \text{O}_2 + \text{O} \\ \text{O}_2 + \text{O} &\rightarrow \text{O}_3 + \text{heat} \end{aligned}$ During the reaction, the UV radiation is converted into heat, so that the stratosphere heats up in relation to the other atmospheric layers. This explains the temperature anomaly in the middle atmosphere, because the absorbed UV radiation acts as a heat source.