Periodic Modulations in Thermospheric Composition by Solar Wind High Speed Streams

We report on periodicities observed in the column density ratio, ΣO/N2, correlated with periodicities in solar wind speed and Kp index. The recently discovered solar-terrestrial connection between rotating solar coronal holes and mass density variations in the Earth's thermosphere by Lei et al. (2008) and Thayer et al. (2008) prompted this study and has led to further insight regarding the thermosphere response to periodic high-speed solar wind streams and recurrent geomagnetic activity. In particular, ΣO/ N2 ratios, measured by the Global Ultraviolet Imager (GUVI) instrument flown on the TIMED satellite, demonstrate strong 9 and 7 day oscillations in 2005 and 2006, respectively, that are well correlated with the solar wind speed and Kp index. More importantly, the ΣO/ N2 ratio response peaks at high latitudes, as opposed to the mass density response being global, indicating that vertical winds are active at the higher latitudes while lower latitudes experience primarily thermal expansion.