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

Integration of the VHF wind profiler data within dual Doppler wind synthesisFrom dual Doppler radar observations, 3D wind field may be retrieved in the commonobserving zone. The retrieving method, used by Petitdidier et al.(2000), was the MANDOP(Multiple ANalytical DOPpler), formerly proposed by Scialom and Lemaître (1990) andadapted to the Alpine case by Tabary and Scialom (2000). This method is based on ananalytical expansion of the wind components along each following axis, east, west, north,south and vertical. The expansion coefficients are retrieved in a minimisation processadjusting the analytical wind components to radial velocities and physical constraints, givenby the anelastic continuity equation and free-slip boundary condition. This method permits toinclude other types of measurements like wind profiler data.Different scenarios were developed to test the impact of the VHF wind components on theretrieved wind fields. The conclusions of this study was the following. The main globalimpact of the WP was very local due to the volume information provided by the WPrelatively to the three-dimensional one observed by the WDR (Fig.1). Nevertheless theimpact became significant and helped better conditioning at the upper boundary level of theretrieved wind field and in a region where the radar beams are nearly collinear.Interpretation of orographic processesDuring the MAP experiment there were 13 days of precipitation over the Lago Maggiorearea. While the general mesoscale flow in the lower troposphere was approaching the Alpinebarrier and rising the foothills, the flow veers and enters in individual river valleys. Thelocations of the VHF wind profiler and the ML WDR, respectively upstream and upslope,permits to determine a veering mean value. The flow is coming from the SouthWest andveers towards the East by 15°. In the upper level, at 5km the direction of the wind is the samefor both radars.2- ReflectivityIn the ML data reduction, an average reflectivity is computed over the VHF and ML radarslocations. Figures 2(a,b,c) present the variation of the radar reflectivites as a function ofaltitude and time. During this period there was a convective activity in this area. Figure 2aand Figure 2b correspond to the reflectivities observed by the ML WDR, respectively overthe ML radar and the WP. The motion of the precipitating system from the WP location tothe ML radar one is observed, as it is expected from the results of the windcomparison(Tabary and Petitdidier, 2002). The enhancement of the WP vertical velocity isconsistent with the convective activity observed by the ML WDR above the WP. Thosesimultaneous observations permit to observe the cloud condition above the wind profiler andthen interpret the WP observations.Figure 2c presents in the same range of altitude the relative reflectivity observed by the WP,pointing vertically. The difference of pattern is not so surprising due to the difference of thetargets, hydrometeors for the WDR and refractive index perturbations induced byatmospheric turbulence for the WP.In case of the WDR involved in MAP, the reflectivity is the result of the Rayleighbackscattering by hydrometeors. Those radars carry out observations up to nearly the top ofthe cloud; at higher altitudes the hydrometeors being too scarce.In case of VHF wind profiler, the volume reflectivity depends on the refractive indexgradient squared (M2), Brunt-Väisälä frequency squared, and the turbulence energy rate ε.−6 ⎛⎞=− ⎜d q+ d dq−T P 15500M 7710 lnθlnθ7800⎟⎝ dz T dz T dz ⎠where p, T, q, θ and z are pressure, temperature, specific humidity, potential temperature andheight respectively. M is very dependent on the water vapor amount , q, and its gradient in255