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ZONAL MEAN WINDS IN THE EQUATORIAL MESOSPHERE AND LOWER THERMOSPHERE OBSERVED BY THE HIGH RESOLUTION DOPPLER IMAGER

This paper presents analyses of mesospheric and lower thermospheric zonal mean winds observed by the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS). Monthly averages of the equatorial zonal mean zonal winds are presented for January 1992 through June 1993. Equatorial zonal winds in the 70–90 km region are dominated by a semiannual oscillation (SAO), ranging from 30 m s−1 (westerly) to −100 m s−1 (easterly). At high latitudes the zonal wind variations are predominantly annual. Above 90 km, the low-latitude flow is easterly at all times, punctuated by a small semiannual variation. This behavior may be related to the deposition of momentum by the diurnal tides.