Energetics and Composition in the Thermosphere

The thermosphere is defined by the high temperatures that occur in its upper regions. These high temperatures result from the absorption of energetic EUV radiation combined with weak in situ cooling. Heat is eventually lost from the upper thermosphere primarily through downward heat conduction. This heating and cooling is modified through a variety of processes, the most important of which, at low and middle latitudes, is heating by compression and cooling by expansion. These thermal processes help to drive the dynamics of the thermosphere, which, in turn, are a major cause of changes in neutral composition. In this paper, we discuss the global changes in heating that arise as a result of high-latitude energy inputs during geomagnetic storms and the ways that we can gain a better understanding of these processes. One of the scientific results of this paper was that low-and middle-altitude heating during a simulated geomagnetic storm was mainly caused by the propagation and dissipation of gravity waves generated near the auroral zone.