Graduate Studies

 

First Advisor

Matthew S. Van Den Broeke

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Adam Houston, Michael Hayes, Ross Dixon

Department

Geosciences

Date of this Version

6-2025

Document Type

Dissertation

Citation

A dissertation presented to the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Earth and Atmospheric Sciences

Under the supervision of Professor Matthew S. Van Den Broeke

Lincoln, Nebraska, June 2025

Comments

Copyright 2025, Devon Jacob Healey. Used by permission

Abstract

Much research over the past decade has revealed that dual-polarization radar is a powerful tool in furthering our understanding of severe storm dynamics and subsequently improving warning strategies for these hazardous events. However, there are currently very few studies examining a particularly prolific severe convective storm mode with dual-polarization radar: quasi-linear convective systems (QLCSs). These storms can occur in any season of the year throughout most of the contiguous United States and can have immense societal impacts. Warning for the hazards produced by QLCSs is currently a significant operational challenge, therefore, research is needed to see if applying dual-polarization radar more in warning strategies for QLCSs will help.

Two novel and complementary modeling studies are presented in this dissertation that examine a particular dual-polarization signature in QLCSs: the differential reflectivity (ZDR) column. The ZDR column has been shown to likely have the most potential in anticipating tornadic potential in supercells. Additionally, the ZDR column is an updraft-associated feature and updrafts are critical for severe weather production in QLCSs. In the first study, the ZDR column is compared between two microphysics parameterization schemes and found to be more realistic in the National Severe Storms Laboratory-Double Moment scheme than the Morrison scheme. Additionally, ZDR columns are often found collocated with a strong mid-level updraft and often found at the same time with a strong low-level updraft in the vicinity. In the second study, the sensitivity of the ZDR column to low-level hodograph shape and size is examined as well as the connection between ZDR columns and low-level mesovortices. ZDR columns are largest when the low-level shear is strongest, yet there is no systematic decrease of column size with decreasing shear. ZDR columns are more likely to be found immediately rearward of a near-surface mesovortex when the low-level hodograph is straight and has large shear. However, ZDR columns away from mesovortices are often more pronounced than when in the vicinity of a mesovortex.

Advisor: Matthew S. Van Den Broeke

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