Lunar tidal winds between 80 and 110 km from UARS/HRDI wind measurements

Recent observations and models show the considerable effects of upward-propagating lunar atmospheric tides on many aspects of the ionosphere-thermosphere system. A key aspect of atmosphere-ionosphere coupling is the wind field in the ionospheric E region (circa 100-150 km), where the dynamo generation of electric fields occurs. Yet, global specifications of lunar tidal winds exist only in theoretical predictions although years of satellite observations on atmospheric winds exist with almost global coverage. In the present paper, we report on quasi-global semidiurnal lunar tidal winds up to 115km from data gathered by the High Resolution Doppler Imager (HRDI) on board the Upper Atmosphere Research Satellite during the early years from 1991 to 1999. The observed lunar semidiurnal tidal winds are consistent with global scale wave model (GSWM) simulations in both amplitude and phase, with maximum amplitudes located between about 40 degrees N-60 degrees N around the solstices. The peak amplitudes of the lunar tidal winds lie in the 10-15ms(-1)range, whereas those simulated by GSWM lie between 15 and 25ms(-1). The smaller HRDI amplitudes are likely due in part to amplitude suppression in construction of the climatological mean resulting from year-to-year phase variability in the lunar tide. It is also possible that wave dissipation is underestimated to some degree in the GSWM.