Thermospheric Global Change during Solar Cycle 24

Recent model developments and a prediction of solar activity for the next solar cycle [Dikpati et al., Geophys. Res. Lett., 33, L05102, 2006] motivate a study of the interaction between solar and anthropogenic forcing of temperature and density in the terrestrial thermosphere. Model results and observational evidence indicate that increasing carbon dioxide levels throughout the atmosphere are causing the thermosphere to slowly cool and consequently decrease in density at altitudes typically populated by objects in low-Earth orbit (about 200 to 800 km). This gradual secular change is still much smaller than effects of solar irradiance and geomagnetic variation, and is furthermore modulated by the solar cycle, with the largest secular changes occurring at solar minimum. By extrapolating the long-term CO2 record and utilizing a solar cycle prediction based on the Dikpati et al. model, we forecast thermospheric temperature and density for solar cycle 24, examine their secular change, and evaluate the prospects for long-term change during this century.