On the response of the exospheric temperature to the auroral heating impulse during geomagnetic disturbances

Abstract

On the basis of an assumed impulse-type energy input at auroral oval due to the particle precipitation, the response of the exospheric temperature T ∞ has been investigated in terms of changes in input energy, geomagnetic indices and latitude under simplified assumptions It is shown that the resulting T ∞ is proportional to the peak heating rate and inversely proportional to the gradient of the atmospheric density. Even during low solar activity and quiet geomagnetic conditions, the precipitated electron energy density in the thermosphere is found in the range of about 1–1.5×10 −6 erg/cm 3 s, reaching to about 3×10 −6 erg/cm 3 s at 2000 K and is easily supported by the solar wind–magnetospheric interaction. The auroral energy inputs lasting less than 2 h or so hardly generate geomagnetic storms. The inhomogeneous energy equation has been solved in horizontal two dimensions in presence of horizontal heat conduction, to study the T ∞ at other latitudes and its time delay with respect to the peak impulse heating time. This time delay is independent of the storm intensity, i.e., proxy geomagnetic indices and is about 6–7 h at low and mid latitudes and about 3 h or less at high latitudes in agreement with recent coupled magnetospheric–ionospheric–thermospheric models and with the available observed values. The diffusion coefficient of horizontal heat conduction deduced is about 7×10 4 m 2/s. The role of the horizontal heat conduction in the energy budget needs further investigation.