Estimation of the equivalent Rayleigh friction in mesosphere/lower thermosphere region from the migrating diurnal tides observed by TIMED

We use Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) global temperature and wind data from 2002 to 2007 to investigate the damping of the diurnal tide. Horizontal winds are measured by TIDI and are calculated from SABER temperature measurements. The determination of tidal winds from SABER temperature depends on the damping and, therefore, the discrepancy between TIDI and SABER determinations of the wind tides can be used to calculate the tidal damping. This damping is approximated here by an equivalent Rayleigh friction (ERF), and it is adjusted to minimize the difference in winds derived from SABER and TIDI data. The results show that during some periods the ERF coefficient can be very large over narrow vertical regions of about 5 km (∼10−5 s−1 in low latitudes and about 10−4 s−1 in midlatitudes). The magnitude and shape of the vertical profiles change with latitude and season. The peak in the vertical profile of ERF is larger and located at a higher altitude in summer than in winter and the ERF coefficients at 40° are stronger than at 20° in both hemispheres. The ERF deduced in this study, without a priori assumption about the mechanism of the damping, shows a seasonal variation that is clearly consistent with the seasonal variation of the zonal mean wind; the maximum ERF generally coincides with the altitudes of strongest wind reversal in the mesopause region.