Modeling the Daytime Energy Balance of the Topside Ionosphere at Middle Latitudes

Recently reported measurements from the Defense Meteorological Satellite Program (DMSP) indicate that the O⁺ temperature in the topside ionosphere is dependent on the fractional H⁺ density. This finding indicates that the mass-dependent energy exchange rate between O⁺ and H⁺ plays an important role in the thermal balance of the topside ionosphere. In this study we utilize the SAMI2 model to retrieve both T_{H⁺} and T_{O⁺} and verify the previously observed dependence of ion temperature on ion composition. The model shows that in the topside at middle latitudes when a single ion is dominant, O⁺ or H⁺ is heated by electron collisions and cooled by conduction as expected. However, in the intervening altitude region where both O⁺ and H⁺ are present, O⁺ is heated by collisions with H⁺ and cooled by conduction, while H⁺ is heated by collisions with electrons and cooled by collisions with O⁺.