Synthetic dual-Doppler analysis of a winter mesoscale vortex

This article presents a detailed examination of the kinematic structure and evolution of the 5 December 1997 winter mesoscale vortex in the vicinity o f Lake Michigan using the synthetic dual-Doppler (SDD) technique. When such a mesoscale event propagates a distance large enough that the viewing angl e from a single-Doppler radar changes by about 30 degrees and the circulati on is sufficiently steady during this time period, then the SDD method can reveal reliable details about the circulation. One such detail of the obser ved vortex was a pattern of convergence and divergence associated with radi al bands, where heavier snowfall was located. Another was the steadiness an d vertical coherence of the derived vorticity and convergence patterns with in the cyclonic circulation On 5 December 1997. the observed reflectivity field remained remarkably ste ady for nearly 2.5 h as the vortex moved southeastward allowing for the app lication of the SDD technique. The reflectivity field exhibited a pronounce d asymmetric convective structure with at least three well-defined, inward- spiraling radial snowbands, and a distinct weak-reflectivity region or "eye " near the center of cyclonic circulation. The SDD results showed the vorte x circulation was composed of a combination of rotation on the meso-beta sc ale and convergence on the meso-gamma scale associated with the embedded ra dial snowbands. Vertical profiles of derived meso-beta -scale. area-mean co nvergence and vorticity suggest that this winter vortex was likely a warm-c ore system, similar to both tropical cyclones and polar lows.