Climatology of Neutral Winds in the Lower Thermosphere Over Millstone Hill

Daytime neutral winds in the lower thermosphere (100-130 km) at 42.5N for four seasons, measured by the ground-based incoherent scatter radar (ISR) at Millstone Hill between 1987 and 2000 and the space-based Wind Imaging Interferometer (WINDII on UARS) between 1992 and 1997, are compared and show excellent agreement. The wind fields are dominated by migrating semidiurnal tides. The observations provide the phase, wavelength, and amplitude of the tides, and the altitude at which the semidiurnal tides become evanescent. The wind speed is significantly lower during winter than during other seasons, and there are minor differences in the tidal phase between the Millstone Hill ISR winds and WINDII winds. The observed winds are also compared to TIME-GCM simulations. TIME-GCM winds are in good agreement with observations for equinoxes, and in reasonable agreement with observations for solstices.