DIURNAL MIGRATING TIDE AS SEEN BY THE HIGH-RESOLUTION DOPPLER IMAGER UARS .1. MONTHLY MEAN GLOBAL MERIDIONAL WINDS/

The high-resolution Doppler imager (HRDI) instrument on board the uppe r atmosphere research satellite measures global winds in the mesospher e and lower thermosphere on a day-to-day basis. The horizontal coverag e of the HRDI data is excellent and provides a unique opportunity to s tudy global-scale dynamic phenomena; however, the local time resolutio n and coverage are limited because of the nature of the satellite samp ling. The lack of local time coverage makes conventional methods of da ta analysis (e.g., Fourier analysis) both difficult and erroneous. An original method of analysis, based on a numerical model of atmospheric thermal tides, is proposed and applied to the HRDI data. The tidal mo del is solved for the tidal oscillations in the meridional wind compon ent. The simulated diurnal meridional tidal winds are used as a first guess in the analysis. The results of the model are adjusted to give m eridional migrating tidal winds that have maximum consistency with HRD I measurements. This technique is used to derive monthly mean tidal os cillations of the meridional velocity. The derived tidal amplitudes sh ow profound seasonal changes that seem to be consistent with gravity w ave breaking theory. The results are compared with MF radar data. It i s found that in the upper mesosphere and lower thermosphere, the tidal amplitudes obtained by HRDI can be bigger than those from MF radars b y a factor of 2.