Thermospheric zonal mean winds and tides revealed by CHAMP

We present direct, global observations of longitudinally averaged CHAMP zonal winds gathered between 2003 and 2007. A diurnal variation dominates the global zonal wind. Westward flows are observed from the early morning through afternoon hours, while eastward flows peak in the evening. A semidiurnal harmonic is also present, with magnitudes that are approximately one third of the diurnal harmonic. The time mean wind indicates westward winds over much of the globe, with weak superrotation (+E, or eastward winds) that is symmetric about the equator during equinox, and confined to the winter hemisphere at solstice. Diurnal and time mean CHAMP winds agree fairly well with the Whole Atmosphere Model. Some differences are observed in the semidiurnal and higherorder tidal winds, that underscore the challenges of modeling the sources, sinks, and mean wind effects upon tides between the surface and 400km.