Matthew Van Den Broeke
Date of this Version
Wood, Michaela J.; Radar Signatures in Tropical Cyclone Tornadic and Nontornadic Supercells, 2023; M.S. thesis, University of Nebraska-Lincoln Digital Commons.
Tropical cyclones (TCs) contain highly-sheared environments that are conducive for supercell thunderstorms. These TC supercells sometimes produce tornadoes, often with little warning. Given the often-close proximity of tornadic and nontornadic TC supercells, environments may not be well-distinguished, pointing to the potential value of radar observations. In this study, dual-polarimetric radar signatures of a sample of TC supercells are examined in the context of known supercell structure and microphysics. Tornadic and nontornadic TC supercells are compared with their midlatitude counterparts, and the environments and characteristic structure of these storms are shown to be notably different. An attempt is made to distinguish differences between tornadic and nontornadic TC supercells that may hold operational promise. Prior research has only examined dual-polarimetric TC supercells using a case study approach; therefore, this study aims to create a more comprehensive picture with a large sample of cases. Differential reflectivity (ZDR) columns remained shallower in TC supercells when compared to their midlatitude counterparts. ZDR columns were also much rarer in TC cases than in midlatitude cases, making ZDR columns an unreliable proxy for updraft characteristics in TC cases. However, no significant differences were present between ZDR columns in tornadic and nontornadic TC supercells. ZDR arcs remained as pronounced in TC supercells as they are in midlatitude cases, with maximum and mean ZDR values within the signatures being larger in TC cases. This is likely due to the increased low-level wind shear in TC cases promoting more effective drop size sorting. Separation angle between the specific differential phase (KDP) foot and ZDR arc was larger in TC supercells than midlatitude supercells, again due to the increased low-level wind shear and drop size sorting. The inverse was seen with a normalized separation distance between the two signatures. Neither separation angle nor distance between the KDP foot and ZDR arc gave an indication of tornadic potential in TC supercells. The key finding from this research is that tornadic TC supercells had significantly stronger low-level mesocyclones as measured by normalized rotation (NROT) than nontornadic TC supercells.
Advisor: Matthew S. Van Den Broeke