A Dual-Polarimetric Analysis of a Large Sample of Left-Moving Supercells

Authors

Ben Schweigert, University of Nebraska-LincolnFollow

First Advisor

Matthew S. Van Den Broeke

Second Advisor

Adam Houston

Third Advisor

Matthew Bunkers

Date of this Version

5-2024

Citation

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, Nebraska, May 2024

Comments

Copyright 2024, Benjamin J. Schweigert. Used by permission

Abstract

Supercells have been researched extensively since they were first described over 50 years ago. They are prolific severe weather producers, responsible for the most severe hail, severe wind gusts, and tornadoes. These rotating thunderstorms require attention from forecasters to protect life and property from their threats, most effectively done with Doppler radars. While extensive amounts of radar-based investigations have been completed, they focused almost exclusively on right-moving (RM) supercells, resulting in a knowledge gap surrounding their counter-rotating (left-moving, LM) partners. This study works to fill the void by developing a dataset of LM supercells and analyzing the dual-polarimetric features observed within. A comparison to a dataset of RM supercells is also conducted. The supercell polarimetric observation research kit algorithm was utilized for automatic dual-pol quantification and visualization. A clear increasing relationship was seen between mesoanticyclone strength and longevity. Differential reflectivity (Z_DR) columns were wider and deeper in RMs, and column area and depth were seen to increase with increasing LM strength and longevity. Z_DR arcs were smaller in LMs than RMs, and was not related to mesoanticyclone strength or longevity. Arcs were more intense in LMs. The arrangement of separation angles between the Z_DR arc and differential phase (K_DP) foot intriguingly showed a bimodal distribution. The angle and separation distance were both smaller in RMs. There was no discernable connections to mesoanticyclone strength or longevity. Inferred hailfall area was on average larger in RM supercells, and increased in area with increasing LM strength. Based on statistical examinations, the Z_DR column and hailfall characteristics show the best promise for operations in terms of radar-based diagnoses of LM supercells. Furthermore, the correspondence of mesoanticyclone strength and longevity can assist in prioritizing thunderstorms in situations with multiple ongoing LM supercells, or convective outbreaks that in part include LM supercells.

Advisor: Matthew S. Van Den Broeke