Periodic modulations in thermospheric composition by solar wind high speed streams

Sigma O/N-2 ratios in the Earth's thermosphere are measured by the Global Ultraviolet Imager (GUVI) on the TIMED satellite, and demonstrate strong 9 and 7 day oscillations in 2005 and 2006, respectively, that are well correlated with the solar wind speed and Kp index. This work builds on the recently discovered connection between rotating solar coronal holes and thermospheric mass density variations. The work described here is the first description of geomagnetically forced periodicities in neutral composition. Furthermore, these observations provide the first definitive proof that the processes creating neutral composition changes during geomagnetic storms occur continuously at all activity levels and all over the world. The Sigma O/N-2 response versus the mass density response indicates the important role of vertical winds at high latitudes while thermal expansion dominates at lower latitudes. Citation: Crowley, G., A. Reynolds, J. P. Thayer, J. Lei, L. J. Paxton, A. B. Christensen, Y. Zhang, R. R. Meier, and D. J. Strickland (2008), Periodic modulations in thermospheric composition by solar wind high speed streams, Geophys. Res. Lett., 35, L21106, doi: 10.1029/2008GL035745.