The Effects of Magnetosheath Electrons on Charge Exchange, Radiation Trapping and Other Atomic and Molecular Processes in the Mid-Day Polar Cusp Thermosphere

Abstract

Magnetosheath electrons precipitating in the mid-day cusp region dissipate most of their energy in the thermosphere above 200 km where atomic species are more abundant than at lower altitudes. Part of the atmosphere where these electrons excite mid-day auroras is also sunlit. The high abundance of atomic species, their longer mean free path and the presence of sunlight in the atmospheric region where mid-day auroras are formed, permit studies of certain interactions among atmospheric constituents, as well as radiation transport process, which cannot be observed in laboratories or in lower altitude night time auroras. Examples of such upper atmospheric processes amenable to investigations in the mid-day cusp region are (i) charge exchange reactions between 0⁺(²D) and N₂, (ii) radiative entrapment of extreme ultraviolet radiation and its effect on auroral emissions, (iii)iresonant scattering of sunlight by atmospheric species, (iv) buildup of vibrationally excited molecules above the level expected from the kinetic temperatures in the thermosphere, (v) variations in the abundance of thermospheric N and He, and (vi) the propagation of atmospheric disturbances from the thermosphere to the mesosphere.