Thermospheric heating away from the auroral oval during geomagnetic storms

Abstract

Model predictions indicate that the high-latitude thermosphere near the F2 peak undergoes strong heating during geomagnetic storms. Experimental studies at middle and equatorial latitudes have indicated that heating occurs during geomagnetic storms, although the overall morphology of these temperature changes is not clear. In this paper we use data from the DE-2 (dynamics explorer) satellite to study this morphology at middle and high latitudes, and then use a simulation of the November 24, 1982 storm, by the NCAR–TIGCM, to compare model output and data on a "one-on-one" basis for an individual orbit in the middle of this storm. Agreement between model and data is good in the winter hemisphere, so we use a thermodynamic diagnostic processor to make a preliminary investigation of the mechanisms by which geomagnetic storms cause temperature increases at lower latitudes. The major conclusions from this work are (i) unlike compositional changes, thermospheric temperature changes do not display a long "tail" into the post-midnight, mid-latitude region; (ii) the pattern of heating during geomagnetic storms is complex, a result of the complicated physical processes that occur during geomagnetic storms; (iii) heating due to advection is approximately balanced by expansion of the gas and downward heat conduction in the postmidnight region; (iv) model predictions for this storm indicate that the greatest temperature increase at 40° N is seen in the dawn sector; (v) early in the storm the strongest compressional heating at latitudes near 40° N is found in the premidnight region, where parcels of air are slowed by sunward ion convection, and consequently converge causing downward winds; (vi) compressional heating also occurs in the afternoon, in a region where expansion of the gas, and hence cooling, occurs during quiet geomagnetic times.