The Existence of Descending Reflectivity Cores in Rear-Flank Appendages of Supercells

Three-dimensional analysis of radar data during VORTEX by Rasmussen et al. (2006) revealed that in some supercells, development of the rear-flank appendage and tornadogenesis was preceded or accompanied by the descent of a reflectivity protuberance pendant from the echo overhang. This phenomenon has been called the Descending Reflectivity Core (DRC), and is often associated with enhanced rear-to-front flow near the surface. In Rasmussen et al. (2006), this feature occurred in some supercells, but not others. However, all cases of tornadogenesis were preceded by a DRC although this study was limited by a small sample of supercells.

The primary purpose of this paper is to discuss what we now know about the DRC by presenting several studies which have not been formally published as of yet. Specifically, the results of a study focusing on DRCs in a large sample of storms are discussed. These DRCs descended in a variety of ways, one of which may be preferred for tornadogenesis. Within this study, the frequency of DRCs is explored within supercells and preceding tornadogenesis. Near surface single-Doppler velocity signatures were investigated during the occurrence of DRCs. Of the 64 supercells included within this study, 59% were DRC producing. 30% of the DRCs preceded tornadogenesis, while 24% of tornadoes followed DRCs.

Finally, a visual observation of a descending reflectivity core (DRC) is presented with accompanying radar data from a WSR-88D on 6 June 2005. The DRC appeared as a dense rain shaft that descended rapidly from the cloud base. Through the use of stereo photogrammetric techniques, it is seen that the rain shaft corresponded with a maximum of reflectivity within a developing hook echo.