Abstract:

This paper examines the sombined mesospheric and thermospheric (50 to 200 km) longitudinally averaged winds measured by the wind imaging interferometer (WINDII) and the high-resolution Doppler imager (HRDI) onboard the Upper Atmosphere Research Satellite. The data analyzed cover 2 years from February 1992 to February 1994 and consist of both day and nighttime WINDII winds obtained fromthe O(¹S) green line emission and mesosphere/lower thermosphere daytime HRDI winds fromthe O₂ atmospheric band/ The combination of the WINDII and HRDI data sets is first justified by comparing all the data in the lower-thermosphere overlap region for days and orbits when both instruments were observing the same volume of atmosphere. The comparison shows good agreement between the teo instruments. An analysis of hte sombined WINDII and HRDI winds during equinox and soltice periods is then performed. The amplification with height of the diurnal tide at equinox and its subsequent decay in the lower thermosphere is clearly demonstrated by the observations. The corresponding bakground (i.e., diurnal mean) zonal wind component exhibits a broad region of easterlies at lower latitudes in the upper mesosphere and lower thermosphere and westerlies at mislatitudes. Above 120 km the mean winds revert to easterlies in the zonal component and a two-celled equator to pole meridional circulation. The soltice circulation is highly asymmetric about the equator in accordance with the interhemispheric difference in solar heating. The reversal of the mesospheric jets as well as the summer to winter hemisphere meridional flow in the middle thermosphere are clearly shown. At soltice a significantly weaker and more hemispherically asymmetric propagating diurnal tide is also evident.