Using the Supercell Polarimetric Observation Research Kit (SPORK) to Examine a Large Sample of Pretornadic and Nontornadic Supercells

Abstract

Previous work examining dual-polarization (dual-pol) radar signatures of supercells has shown that differential reflectivity (ZDR) column area, hailfall area and specific differential phase (KDP)–ZDR separation angles may differ between tornadic and nontornadic storms. However, these signatures often can be difficult to quantify quickly enough to enable their use in forecasting operations, and little work has been done examining how these characteristics vary with environmental parameters in large samples of observed storms. This paper introduces the Supercell Polarimetric Observation Research Kit (SPORK) as an update to our automated ZDR arc-detection algorithm. This update adds the capability to identify ZDR column and inferred hailfall signatures in supercells automatically, and quickly quantify their characteristics. Dual-pol metrics calculated by SPORK are compared to manually calculated dual-pol metrics from previous work. SPORK is run on a large sample of supercells to examine whether SPORK-calculated dual-pol metrics exhibit the same differences between tornadic and nontornadic supercells seen in manual analyses. Storm-mean dual-pol metrics obtained from SPORK also are used to evaluate how supercell dual-pol metrics vary with different environmental parameters. Results from SPORK support previous findings that tornadic supercells have larger ZDR column areas, smaller hailfall areas, and larger KDP–ZDR separation angles than nontornadic storms. Additionally, ZDR columns tend to be larger and deeper in more conditionally unstable environments. Hailfall areal extents are larger in environments with lower environmental 0ºC levels, higher LCLs and LFCs, and less SRH. Separation angles are larger in environments with larger low-level shear vectors, SRH and lower lifted condensation levels (LCLs) and levels of free convection (LFCs). However, none of these correlations exceed r = 0.52. Overall, our results indicate that SPORK can quantify supercell dual-pol signatures accurately enough to detect potentially useful differences between dual-pol signatures of pretornadic and nontornadic supercells, and provide a first look at how dual-pol signatures vary with environmental characteristics in a large sample of supercells.