Thermosphere

Definition

The region of an atmosphere called the thermosphere is characterized by an increase in neutral temperature as a function of altitude and asymptotes to a relatively constant temperature. The corresponding neutral atmospheric density is decreasing with altitude. The top of the region is bounded by the thermopause (or exopause/exobase), defined to be the region where the mean free path of particles is longer than a scale height. The bottom boundary is the mesopause, which is defined by the change in the thermal gradient from negative to positive (i.e., temperature begins to increase above the mesopause).

Energy is transported between the lower atmosphere (i.e., troposphere, mesosphere) and space (exosphere) through the thermosphere. The processes involved in the energy transport heavily influence the behavior and structure of the thermosphere. The relative importance of these processes depends greatly on the planetary environment and is related to how energy is absorbed,...