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

Figure 1: composite day (13 days) of the vertical velocity (a) and of the Doppler spectralwidth (b) deduced from the UHF and sodar measurements (200 to 600 m height).vertical velocity (a) and spectral width (b) provided by UHF radar and sodar. Compared withsodar data, there is a systematic UHF negative vertical velocity bias during the day time. Butthe spectral widths of the UHF and sodar present nearly the same time variation.Girard et al (2003) has shown the possibility of the RASS technique to investigate thedependence of the Doppler spectral width of the sound velocity with the turbulence of themixed layer. The spectral width of the vertical beams of the sound is related to the variance ofradial velocity as: V '2 = ( V ' W ') 222. With V ' = T ' , this expression becomes :r s +422 K 2'2 KV ' r = T'W 2 T'W '42v + + v . This expression shows that the variance of the soundV 2V ssspectra is function of the variance of the virtual temperature (Tv), of the variance of the airvertical velocity (W’) and of the sensible heat flux ( TvW ' ). It is necessary to determine twoterms by others methods to obtain the third. The contribution of the three terms to thetotal variance has been estimated to 20 to 30 % for the variance of virtual temperature,to 40 to 60 % for the variance of vertical velocity: and to 30 to 40 % for the virtualsensible heat flux with comparison with data in situ obtained on mast.sK44V2sVNormalized height (Z/Zi)1,210,80,60,40,2UHFaircraft00 0,2 0,4 0,6 0,8 1Momentum fluxes (10-2 m2/s2)Figure 2: (a and b)Profiles of the two components of the momentum fluxes deduced fromUHF during TRAC experiment ( 19/06/98). © comparison of the total fluxes with the aircraftdata.311