Global Observations of Thermospheric Lunar Tidal Winds

Friday, 19 December 2014
Ruth Segal Lieberman, GATS-Inc., Boulder, CO, United States, David C Fritts, GATS Inc., Boulder, CO, United States, Nicholas M Pedatella, National Center for Atmospheric Research, Boulder, CO, United States and Eelco Doornbos, Delft University of Technology, Aerospace Engineering, Delft, Netherlands
We present direct observations of the lunar semidiurnal tide in GOCE 250 km zonal winds and in CHAMP 350 km zonal winds during low solar activity. The migrating semidiurnal lunar tide (M2) has a global extent, with amplitudes of about 10 m/s at equatorial latitudes. Amplitude maximima appear twice yearly in CHAMP winds (2006-2008), generally around equinox. In GOCE winds (2010-2011), on the other hand, the strongest amplitudes appear between October--February. The magnitudes of M2 are consistent with numerical predictions in WACCM-X. However, WACCM-X simulates only one global-scale maximum during January--March, with the strongest amplitudes at high latitudes. The reasons for the model and observational discrepancies cannot be fully determined, and may be related to differences in the zonal mean zonal winds.