Common-volume measurements of mesospheric winds: 2. Small scale structure implications

Two common volume experiments were conducted in August 1996 and July 1997 between the Durham meteor wind radar (43.1°N, 70.9°W) and the Millstone Hill incoherent scatter radar, (42.6°N, 71.5°W) to compare the techniques in measuring neutral winds at an altitude of 100 km. For this comparison the vertical winds are assumed to be zero and only the horizontal components of the radar line of sight velocities are used. Analysis of the data reveals overall general agreement, but some large deviations in the wind components are observed at specific times and these are examined closely. Error analysis of the radar measurements is presented here, and emphasis is placed on the careful delineation of the effect of spatial variations in the wind field observed by the two radars. Since the spatial resolution of both radars is<3 km both horizontally and vertically, some of the three dimensional properties of the horizontal wind component can be estimated. For the incoherent scatter radar with its narrow steerable beam, the spatial location of the sampling points could be chosen; however, finer sampling of the wind field results in more temporal smearing due to the fixed measurement time for each point. For the meteor radar the spatial sample points occur randomly within the system beam since they depend on the chance location of observed meteor trails. Both systems spatially undersample the wind field in most cases, but with careful consideration of the system errors for both radars, it is shown that small scale (～10 km) wind variations must exist at these altitudes with rms velocity differences of ～25 m/s.