Recovery of the three-dimensional wind fields over complex terrain using multiple-Doppler radar data

A variational-based multiple-Doppler radar synthesis method is extended by which one can synthesize the three-dimensional wind field over complex topography. In order to take into account the influence imposed by a non-flat surface, the immersed boundary method (IBM) is implemented. Both Dirichlet and Neumann boundary conditions for the wind fields can be incorporated. The wind fields above the terrain are obtained by variationally adjusting the solutions to satisfy a series of weak constraints, including the multiple-radar radial velocity observations, anelastic continuity equation, vertical vorticity equation, background wind, and spatial smoothness terms. It is found from experiments using model-simulated data that the flow structures over complex orography can be successfully retrieved using radial velocity measuruments from multiple Doppler radars, while the major advantages of the original synthesis method are still retained. That is, the winds along and near the radar baseline are well retrieved, and the resulting three-dimensional flow fields can be used directly for vorticity budget analysis, and to infer the pressure and temperature distributions through the thermodynamic retrieval algorithm. This method is also tested using the radar data collected during SoWMEX, conducted from May to June, 2008 in Taiwan, and reasonable results are obtained.