Seasonal variability of the diurnal tide in the mesosphere and lower thermosphere over Maui, Hawaii (20.7°N, 156.3°W)

The seasonal variability of the diurnal tide in the mesosphere and lower thermosphere over Maui, Hawaii (20.7°N, 156.3°W), is investigated using meteor radar horizontal wind measurements from the years 2002 to 2007. The semiannual oscillation (SAO) of tidal amplitudes is dominant above ∼88 km, with amplitudes at equinoxes 2-3 times larger than at solstices. Below 88 km, the annual oscillation (AO) dominates, and its magnitude is smaller than the SAO. The AO dominates in the phase variation of the diurnal tide, which advances in winter and lags in summer as compared with equinoxes. The vertical wavelength also has a noticeable seasonal variation with shorter vertical wavelengths found at equinoxes. The reconstructed diurnal tide from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) Doppler interferometer (TIDI) and Sounding the Atmosphere using Broadband Emission Radiometry (SABER) measurements is compared with the meteor radar observation, and a consistency is found in the seasonal variation of the tidal amplitude. On the basis of the TIDI and SABER measurements, the migrating diurnal tide (DW1) is the dominant tidal component, while three other nonmigrating tides, DW2, DS0, and DE3, are nonnegligible. The seasonal variation of the diurnal tide is well captured by the global scale wave model and the Whole Atmosphere Community Climate Model, although important discrepancies still exist.