Radar Signatures in Tropical Cyclone Tornadic and Nontornadic Supercells

Authors

Michaela Wood, University of Nebraska-LincolnFollow

First Advisor

Matthew Van Den Broeke

Date of this Version

Spring 5-2-2023

Citation

Wood, Michaela J.; Radar Signatures in Tropical Cyclone Tornadic and Nontornadic Supercells, 2023; M.S. thesis, University of Nebraska-Lincoln Digital Commons.

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Earth and Atmospheric Sciences, Under the Supervision of Professor Matthew S. Van Den Broeke. Lincoln, NE: May 2023

Copyright © 2023 Michaela J. Wood

Abstract

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 (Z_DR) columns remained shallower in TC supercells when compared to their midlatitude counterparts. Z_DR columns were also much rarer in TC cases than in midlatitude cases, making Z_DR columns an unreliable proxy for updraft characteristics in TC cases. However, no significant differences were present between Z_DR columns in tornadic and nontornadic TC supercells. Z_DR arcs remained as pronounced in TC supercells as they are in midlatitude cases, with maximum and mean Z_DR 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 (K_DP) foot and Z_DR 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 K_DP foot and Z_DR 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