Modeling the daytime energy balance of the topside ionosphere at middle latitudes

Abstract

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 TH+ and TO+ 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+.

Measurement of Individual H+ and O+ Ion Temperatures in the Topside Ionosphere

“…Also, in Figure , there are regions where the fractional H + concentration is greater than 20% and where T H+ recovered from our new routine is higher than T O+ by about 200 K. This result agrees with the model results of Hsu and Heelis () confirming that O + is heated by collisions with the electrons and collisions with the lighter H + ions. The plasma is O + dominant in the summer hemisphere as the O + /H + transition height resides above the spacecraft and interhemisphere transport may be recognized by the ram velocity indicating plasma flow from the summer hemisphere to the winter hemisphere across the equator.…”

“…Hsu and Heelis (2017a) report that the O + temperature is larger in the topside when H + is the dominant constituent, than when O + is itself dominant. Hsu and Heelis (2017b) also show that the relationship between the O + temperature and the topside ion composition is consistent with the expected heat exchange between H + and the electrons.…”

“…Note that DMSP F15 is a polar-orbiting night-ascending satellite; it moves from north to south on the dayside such that negative ram velocity indicates south to north flow. The plasma flow across the equator may produce adiabatic heating and cooling, but the effects on the daytime plasma temperatures are small when the plasma is being actively heated by photoelectrons (Hsu & Heelis, 2017b). Figure 5 shows the average distribution of key ion parameters as a function of geographic longitude and geographic latitude for the northern winter (left panels) and northern summer (right panels) months in 2005.…”

“…During the daytime, ion temperatures are determined primarily by the flow of heat from electrons to ions that is balanced by the flow of heat from the ions to the neutral gas, which is controlled by the integrated effect of collisional cooling to the neutrals in the region below (Hsu & Heelis, ). We have previously noted that the additional adiabatic heating and cooling mechanisms arising from motions of the plasma have only a small effect on daytime plasma temperatures.…”

“…Note that DMSP F15 is a polar‐orbiting night‐ascending satellite; it moves from north to south on the dayside such that negative ram velocity indicates south to north flow. The plasma flow across the equator may produce adiabatic heating and cooling, but the effects on the daytime plasma temperatures are small when the plasma is being actively heated by photoelectrons (Hsu & Heelis, ).…”