Proceedings with Extended Abstracts (single PDF file) - Radio ...

Figure 2: Mean zonal and meridional winds (left and middle) derived from standard DBSexperiments and radial velocities (right) obtained with interleaved oblique narrow beams(HPFW=6.6 ◦ ) at 17.2 ◦ off-zenith angle during dual-beamwidth observation.The mean horizontal winds were less than 10 m/s during the whole experiment periodon April 23, 2003 (Figure 2). Since the velocities were very small the correction term forbeam and shear broadening used in the single-beamwidth method was negligible (middlepanel of Figure 3) and σ 2 turb ≈ σ 2 obs .The 3-hour mean profile of σ 2 turb obtained from the dual-beamwidth method shownin Figure 4 depict velocity variances between 5 and about 15 m 2 /s 2 below 78 km wherecontributions from specular reflections should be small or negligible. With a mean Brunt-Vaisala frequency of 0.018 for the altitude range between 65 and 84 km based on a meantemperature profile for April after falling sphere measurements at Andenes (Lübken,1999) these turbulent velocity variances can directly be converted into turbulent kineticenergy dissipation rates. These values between 10 and 60 mW/kg (top axis in the rightpanel of Figure 4) are in reasonable agreement with rocket observations during springtransition (Müllemann et al., 2002). The first results of simultaneous 2BW and 1BWobservations during low wind speed conditions are in good agreement. Further tests ofFigure 3: Profiles of the observed spectral widths σ 2 obs (left) from the NW and SE narrowbeam experiments, the correction term σ 2 corr (middle) and the turbulent spectral widthσ 2 turb (right) obtained with the single beam width method.247