Dual-Doppler wind analysis of convective storms using the vertical vorticity equation

The dual-Doppler analysis of the vertical velocity field in convective storms has long been fraught with difficulty. One of the main problems is that the lowest scan of the radars may be a kilometer or more above the surface of the earth, where the impermeability condition could safely be applied. Our work focuses on a new method of dual-Doppler wind analysis, with an emphasis on improving the retrieval of the vertical velocity field in the presence of substantial low-level data voids. The analysis proceeds in a three-dimensional variational (3DVAR) framework with the anelastic form of the vertical vorticity equation imposed along with traditional constraints of mass conservation and smoothness. The method is general enough to include data from multiple radars but tests have thus far been restricted to two radars. In previous experiments with a Beltrami flow solution of the Navier-Stokes equations, incorporating the vorticity constraint improved the retrieval of the vertical velocity field in the absence of low-level (< 1.5 km AGL) radial wind data.

Experiments with emulated radial wind observations of a numerically-simulated supercell, as well as with real dual-Doppler observations of the 8 May 2003 Oklahoma City tornadic supercell, will be presented. Special attention will be given to the impact of accounting for the intrinsic evolution of the wind and vorticity fields.