A UAS-centered Investigation of Vorticity Characteristics and Cold Pool Structure Across Forward and Left-flank Boundaries in Supercells

Authors

Mark R. De Bruin, University of Nebraska-LincolnFollow

First Advisor

Adam L. Houston

Committee Members

Matthew Van Den Broeke, Clinton Rowe

Date of this Version

7-2025

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 Adam L. Houston

Lincoln, Nebraska, July 2025

Comments

Copyright 2025, Mark R. De Bruin. Used by permission

Abstract

Supercell internal boundaries are the locus of tornadogenesis; thus, understanding the characteristics of these boundaries, particularly in terms of vorticity, is important for identifying the role they play in tornado formation. Insight into the overall characteristics of internal boundaries and their possible role in tornadogenesis have been driven by studies reliant on numerical modeling-based experiments. Observational studies often neglect above-surface conditions or, when these observations are made, lack the spatial resolution to resolve boundary characteristics. During TORUS (Targeted Observation by Radars and UAS of Supercells) 2019 and TORUS-LItE (TORUS Left-flank Intensive Experiment) 2023, uncrewed aircraft systems (UAS) and mobile mesonets collected in-situ kinematic and thermodynamic observations across left and forward flank boundaries. Three TORUS and TORUS-LItE cases are analyzed herein with the goal of updating understanding of supercell internal boundaries. This analysis reveals that the strongest near-surface vertical vorticity is typically collocated with enhanced streamwise vorticity, baroclinic generation, and gradients in vertical motion and equivalent potential temperature. Horizontal gradients in vertical motion distributed over scales of several hundreds of meters are present in all three cases and made appreciable contributions to horizontal vorticity. Analysis of the 26 May 2023 case reveals a likely streamwise vorticity current (SVC) embedded in the head of a density current-like feature. Comparable structures are observed in the left flank boundaries of the 11 June 2019 case, but with differences in cold pool shape and pressure perturbations. In fact, lack of a meaningful pressure jump in the 26 May 2023 and 12 June 2023 cases are the primary reason the boundaries in these cases cannot be classified as a true gust front.

Advisor: Adam L. Houston