COMBINED MESOSPHERE THERMOSPHERE WINDS USING WINDII AND HRDI DATA FROM THE UPPER-ATMOSPHERE RESEARCH SATELLITE/

This paper examines the combined mesospheric and thermospheric (50 to 200 km) longitudinally averaged winds measured by the wind imaging int erferometer (WINDII) and the high-resolution Doppler imager (HRDI) onb oard the Upper Atmosphere Research Satellite, The data analyzed cover 2 years from February 1992 to February 1994 and consist of both day an d nighttime WINDII winds obtained from the O(S-1) green line emission and mesosphere/lower thermosphere daytime HRDI winds from the O-2 atmo spheric band, The combination of the WINDII and HRDI data sets is firs t justified by comparing all the data in the lower-thermosphere overla p region for days and orbits when both instruments were observing the same volume of atmosphere. This comparison shows good agreement betwee n the two instruments. An analysis of the combined WINDII and HRDI win ds during equinox and solstice periods is then performed. The amplific ation with height of the diurnal tide at equinox and its subsequent de cay in the lower thermosphere is clearly demonstrated by the observati ons. The corresponding background (i.e., diurnal mean) zonal wind comp onent exhibits a broad region of easterlies at lower latitudes in the upper mesosphere and lower thermosphere and westerlies at midlatitudes . Above 120 km the mean winds revert to easterlies in the zonal compon ent and a two-celled equator to pole meridional circulation. The solst ice circulation is highly asymmetric about the equator in accordance w ith the interhemispheric difference in solar heating. The reversal of the mesospheric jets as well as the summer to winter hemisphere meridi onal flow in the middle thermosphere are clearly shown. At solstice a significantly weaker and more hemispherically asymmetric propagating d iurnal tide is also evident.