Sources and sinks of energy in the lower thermosphere

The sources and sinks of energy in the subauroral lower thermosphere (80-150 km) were investigated. Heating and cooling rates due to molecular thermal conduction were calculated using the U.S. Standard Atmosphere, including variations with altitude, latitude, season, and solar activity. Molecular thermal conduction cools the atmosphere above (typically) 125 km and heats below, although the crossover altitude varies strongly with solar activity. Solar photon absorption in the 40 to 3000A region was calculated, with allocation of the initially absorbed energy into ionization, dissociation, excitation, and direct heating. These calculations were done as a function of altitude, latitude, season, and wavelength.