Midlatitude electron and ion temperatures at sunspot minimum

Abstract

Midlatitude F-region electron temperature profiles, determined by ground-based radar methods, indicate a positive gradient at all altitudes up to at least 700 km at sunspot minimum. This is not in accord with current theoretical ideas on the problem of the thermal balance in the ionosphere. According to these ideas the electron temperature should be almost isothermal above 300 km altitude because of the absence of significant heat input at these altitudes and the high thermal conductivity of the electron gas. Thus the results suggest the existence of heat sources above the ionosphere. The diurnal and seasonal variations of the electron temperature and the gradient at 500 km altitude are consistent with a model of photoelectron escape into the protonosphere which gives rise to this heating. Previous theoretical estimates put the energy deposited above 500 km by this means at 10 9 eV/cm 2/sec. The experimental results imply, in winter, a flux of ~6 × 10 9 eV/cm 2/sec and it is presumed that the theoretical value is too low because the number of escaping particles has been under-estimated.