Climate Change Affects the Thermosphere
Satellite drag coefficient variation over altitude and time has important implications for the determination of the secular variation of thermospheric density. Recent studies have detected a secular decrease in density over several sunspot cycles as the concentration of CO2 has increased in the atmosphere. The related change in the thermospheric atomic oxygen concentration implies a change in the drag coefficients of satellites. Studies that use satellite drag to infer densities should use the appropriate physical drag coefficients corresponding to the varying ambient atomic oxygen concentration.
Magnetospheric Energy Affects Satellite Drag
Density variations with latitude and universal time have shown the influence of the energy input from the magnetosphere to the dayside auroral zone at geomagnetically quiet times. That input is further substantiated by the observation of five collocated phenomena: The region of charged particle precipitation; field-aligned currents; the region of the red dayside aurora; a sharp peak in ionospheric electron concentration; and a density bulge related to the magnetospheric dayside cusp. A global semi-empirical density model which includes this high-latitude energy source will soon be available.
Reentry through Transitional Flow
The final few orbits of a reentering satellite are difficult to predict. Important issues include the changing gas-surface interaction as the satellite moves from the region of free-molecular flow to the region of transitional flow. The study of the reentering orbits of numerous satellites has shed light on this difficult regime and reentry prediction improvements have been made for 3 classes of objects. See http://andromeda.isti.cnr.it/srp/ for a complete list of all related publications.