Introduction: The Observational Basis

Meteorologists conventionally divide the atmosphere between 0–80 km into three layers based on the vertical gradient of temperature (Fig. 1.1). In order of increasing elevation these are the troposphere, the stratosphere, and the mesosphere, respectively. In the troposphere and mesosphere the temperature generally decreases with height, while the lower stratosphere is nearly isothermal and the upper stratosphere has a positive temperature gradient with height. The troposphere and the stratosphere are separated by the tropopause, a level of temperature minimum which varies in height from about 15 km at the equator to 9 km at the poles. The stratosphere and mesosphere are separated by the stratopause, a level of temperature maximum which occurs near 50 km. The mesosphere is itself bounded above by the mesopause at about 80 km which is a level of temperature minimum similar to the tropopause. Thus, the troposphere and the mesosphere are regions of relatively low static stability while the stratosphere has relatively high static stability. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.