Rates of electron cooling in the upper atmosphere

Abstract

The cooling of thermal electrons in the ionosphere by excitation of the fine structure energy levels of ground-state atomic oxygen is considered. From the evidence of theoretical studies of the fine structure transition strengths and from modelling of plasma temperatures in the ionosphere, it is concluded that the fine structure cooling must be included for calculation of reliable values of electron temperature, particularly under sunspot minimum conditions. Debate continues on the precise value for the cooling rate. The rate depends on whether or not the energy levels are in thermodynamic equilibrium; ionospheric simulations of electron temperature are hampered by uncertainties in the heating rate and in other cooling rates.