Global observations of thermospheric lunar tidal winds

• Global-scale M2 amplitude maxima appear during equinoxes
• WACCM-X M2 maxima appear only in northern hemisphere winter.
• The discrepancy may be related to zonal mean wind structure below the turbopause.

We present direct observations of the semidiurnal lunar tide zonal winds at 260 km and 350 km during low solar activity in 2007–2008, and 2010–2011. The migrating semidiurnal lunar tide, or M2, is a global feature with amplitudes of about 10 m s−1 at equatorial latitudes, and 20 m s−1 at high latitudes. Amplitude maxima appear twice yearly, between February and April and between August and November. M2 amplitudes during 2007–2008 are about 20% stronger than those during 2010–2011. These magnitudes are consistent with numerical predictions in WACCM-X. However, only one annual global-scale maximum is simulated during January–March.