Synthetic Dual-Doppler Analysis of a Winter Mesoscale Vortex

Abstract

This article presents a detailed examination of the kinematic structure and evolution of the 5 December 1997 winter mesoscale vortex in the vicinity of Lake Michigan using the synthetic dual-Doppler (SDD) technique. When such a mesoscale event propagates a distance large enough that the viewing angle from a single-Doppler radar changes by about 30° and the circulation is sufficiently steady during this time period, then the SDD method can reveal reliable details about the circulation. One such detail of the observed vortex was a pattern of convergence and divergence associated with radial bands, where heavier snowfall was located. Another was the steadiness and vertical coherence of the derived vorticity and convergence patterns within the cyclonic circulation. On 5 December 1997, the observed reflectivity field remained remarkably steady for nearly 2.5 h as the vortex moved southeastward allowing for the application of the SDD technique. The reflectivity field exhibited a pronounced 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 vortex circulation was composed of a combination of rotation on the meso-? scale and convergence on the meso-? scale associated with the embedded radial snowbands. Vertical profiles of derived meso-?-scale, area-mean convergence and vorticity suggest that this winter vortex was likely a warm-core system, similar to both tropical cyclones and polar lows.