Spatiotemporal Characterization of ZDR Column Behavior in X-Band Radar Observations of Potentially Tornadic Storms

The primary objective of this research is to characterize distinct differential reflectivity Z_DR column behavior prior to tornadogenesis (failure) in X-band radar observations of supercells. While there has been extensive analysis of Z_DR columns and what they indicate about convective updraft evolution, less is understood about changes and characteristics within Z_DR columns and their association with tornadogenesis. It is postulated that refined conceptual models of polarimetric radar signatures in potentially tornadic storms will lead to fewer missed detections of imminent tornadogenesis. This research will look to discern distinct changes in Z_DR columns prior to tornadogenesis. We examine in detail Z_DR observations of three supercells observed at high spatiotemporal resolution with X-band polarimetric radar, two of which were tornadic supercells and one of which was a nontornadic supercell. We also examine a 30-member ensemble of simulated supercells (both tornadic and nontornadic) and their attendant Z_DR columns. Z_DR columns are characterized by height, intensity, and areal coverage just above the 0 degree C level. It is hypothesized Z_DR columns will show distinct changes in height, intensity, and areal coverage in the 5 to 0 minutes prior to tornadogenesis (failure). Results from the simulations indicate Z_DR column area and height both increase, on average, prior to tornadogenesis, whereas there was no appreciable change in these metrics for tornadogenesis failure. This result stands in contrast to results from our observational analysis, where there were no consistent, distinguishable changes in Z_DR column metrics prior to tornadogenesis versus failure. This research pinpoints Z_DR column features that can be the focus of future study, either through field observations and/or numerical simulations.