Differentiating Between Tornadic and Nontornadic Supercells Using Polarimetric Radar Signatures of Hydrometeor Size Sorting

Abstract

Supercell storms are the most prolific producers of violent tornadoes, though only a fraction of supercells produce tornadoes. Past research into the differences between tornadic and nontornadic supercells have provided some insights but are of little utility to a real-time warning decision process. Operational weather radars provide consistent observations in real time, but conventional radar techniques have not been able to effectively distinguish between tornadic and nontornadic supercells. After the national radar network upgrade to polarimetric capabilities in 2013, a polarimetric signature frequently observed in supercells is the separation of low-level enhanced differential reflectivity Z DR and specific differential phase K DP regions. We analyzed this signature in tornadic and nontornadic supercell cases and found that, although the separation distances are similar, the separation orientations are statistically significantly different. Tornadic supercells have orientations more orthogonal to storm motion and nontornadic supercells have more parallel orientations. Possible reasons for these differences are discussed. Plain Language Summary Supercell storms are responsible for a vast majority of violent tornadoes, but most supercells do not produce tornadoes at all. Finding differences between supercells that produce tornadoes and those that do not has been a goal of meteorologists for several decades and is important for issuing tornado warnings. Previous research has either used computer simulations or studied specific storms from specialized field campaigns. Neither of these are useful in a realistic tornado warning process. Weather radars provide constant monitoring of supercells, but techniques from the past few decades have been unsuccessful in finding differences between supercells that produce tornadoes and ones that do not. The national radar network was recently upgraded in 2013 and has provided new information. A new signature from the upgraded network is the separation of regions with large values of two different radar variables, which is analyzed in this study in a large number of tornadic and nontornadic supercells. We found that the separation distances are similar but the orientations are significantly different between tornadic and nontornadic supercells.

Polarimetric Radar Characteristics of Tornadogenesis Failure in Supercell Thunderstorms

“…Recent research has indicated some promising results linking a large Z DR -K DP separation angle to tornadic potential in supercell storms, e.g., [26,37]. In this study, the separation angle is nearly identical between pre-tornadic and pre-TGF storms (Table 4).…”

Idealized Model Simulations to Determine Impacts of Storm‐Relative Winds on Differential Reflectivity and Specific Differential Phase Fields

“…Further, regions of enhanced K DP can be censored out if they have reduced values of co‐polar correlation coefficient. As such, we have advocated for using an area‐based approach for identifying low‐level Z DR and K DP enhancement regions in observations (Loeffler & Kumjian, 2018; Loeffler et al., 2020). Loeffler and Kumjian (2018) identified two components of this Z DR − K DP separation which comprised their “separation vector": the distance and orientation of separation.…”

“…A recent study by Loeffler et al. (2020) showed that tornadic supercells tended to have separation orientations closer to perpendicular to storm motion, while nontornadic supercells tended to have orientations closer to parallel to storm motion.…”

“…Loeffler and Kumjian (2018) used what they called the "separation vector" which is comprised of the separation distance and the orientation between the two enhanced regions. A recent study by Loeffler et al (2020) showed that tornadic supercells tended to have separation orientations closer to perpendicular to storm motion, while nontornadic supercells tended to have orientations closer to parallel to storm motion.…”

Polarimetric Size Sorting Signatures in the Convective Regions of Mesoscale Convective Systems in PECAN: Implications on Kinematics, Thermodynamics, and Precipitation Pathways

“…The second uncertainty is the role of updrafts. While both updrafts and storm‐relative winds can lead to sustained size sorting (Kumjian & Ryzhkov, 2012), previous studies (e.g., DMR15; LDL20; Loeffler et al., 2020) mostly focused on storm‐relative winds. These studies implicitly assumed that the effect of storm‐relative winds overwhelmed that of the updrafts.…”