Spatiotemporal Variability of Differential Reflectivity (ZDR) Columns Due to Environment in Tornadic and Nontornadic Supercells

Authors

• Adrianne J. Engel, University of Nebraska-LincolnFollow

First Advisor

Matthew S. Van Den Broeke

Committee Members

Adam Houston, Liang Chen, Mark Anderson

Date of this Version

5-2026

Document Type

Thesis

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 2026

Comments

Copyright 2026, Adrianne J. Engel. Used by permission

Abstract

Polarimetric signatures have been of interest to researchers and operational forecasters since the completion of the WSR-88D network upgrade in 2013. Differential reflectivity (Z_DR) columns, which are collocated with supercell updrafts, are the focus of this study. Microphysical distributions within these signatures can be used to infer updraft strength and elucidate the processes responsible for updraft intensity and evolution. Z_DR column depth, areal extent, and variability of these metrics through space and time are assessed in a dataset of 114 nontornadic and tornadic supercells. Means of column metrics in nontornadic, non-tornado-producing, and tornado-producing analysis times are evaluated for how they relate to one another and as a function of the environments in which they occur.

Columns associated with ongoing tornadoes were significantly deeper, wider, and less variable compared to those in nontornadic storms, indicative of stronger and more stable mid-level updrafts associated with tornadoes. Non-tornado-producing analysis times captured the parameter space of column depth, area, and variability between the other two convective categories. Columns and, subsequently, updrafts, were larger, stronger, and less variable in environments characterized by greater instability. Stronger shear generally had a positive impact on Z_DR column size, although the layers in which it was most impactful varied by convective category. Supercell composite parameter and significant tornado parameter effectively differentiated Z_DR column structure and behavior as it relates to updraft intensity between tornadic and nontornadic cases, which is consistent with prior work.

These findings underscore the role of environmental thermodynamic and kinematic factors in modulating supercell updraft characteristics and highlight the utility of Z_DR columns as proxies to infer updraft and mesocyclone intensity, and, to a lesser degree, tornado potential. 

Advisor: Matthew S. Van Den Broeke