Cataloging Rapid Scan Observations of ZDR Columns in Supercells

The height and intensity of a ZDR column have been hypothesized to have a strong correlation to a supercell’s updraft strength, which is pertinent for tornadogenesis. However, the volume coverage pattern used by the National Weather Service WSR-88D during severe weather only revisits the mid-levels (2 to 6 km AGL) every 5 to 6 min, preventing detailed study of ZDR column behavior immediately preceding tornadogenesis. Numerous polarimetric radar observations of supercell thunderstorms and tornadoes have been captured over the years by various research groups, and some of these data sets (e.g., VORTEX2) are now available in the public domain.

As part of an ongoing effort to study polarimetric tornado precursor signatures, we examine these radar data sets to construct a catalog of high temporal resolution supercell ZDR columns. Following automated identification of each ZDR column, a set of characteristics (height, intensity, areal coverage, and longevity) are evaluated in order to quantitatively associate the effects of these properties on tornado formation or failure.

We will present our current catalog of rapid-scan polarimetric observations of ZDR columns, and invite additional contributions from the community. At the time of the conference, we will have examined cases from VORTEX2 along with PX-1000 and RaX-Pol data sets. Our long-term objectives are to enhance understanding of the dynamics and microphysics of potentially tornadic supercells, as well as identify possible tornado precursor signatures with operational utility.