A comparison between mesospheric wind measurements made near Christchurch (44 degrees S, 173 degrees E) using the high resolution doppler imager (HRDI) and a medium frequency (MF) radar

We report on the comparison of winds measured by a medium frequency (MF) ra dar near Christchurch, New Zealand, and by the high resolution doppler imag er (HRDI). Previous comparisons have: demonstrated that there can be signif icant differences in the winds obtained by the two techniques, and our resu lts are no different. However, these data show relatively good agreement in the meridional direction, but large differences in the zonal direction, wh ere the radar is regularly measuring the zonal wind as too easterly. To do the comparison, overpasses from the satellite must be obtained when it is c lose to the radar site. The radar data are averaged in time around the over pass because we know the radars sample phenomena which have spatial and tem poral scales which make them invisible to HRDI. There are a limited number of overpass comparisons which limit our confidence in these results, but a detailed analysis of these data show that the proximity of the overpass is often an important factor in the differences obtained. Other factors examin ed include the influence of the local time of the overpass, and the amount of radar data averaged around the overpass time.