Multi-case Study of Left-flank Boundaries within Supercells

Authors

Peyton B. Stevenson, University of Nebraska-LincolnFollow

First Advisor

Adam L. Houston

Committee Members

Matthew Van Den Broeke, Clinton Rowe

Date of this Version

7-2024

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 2024

Comments

Copyright 2024, Peyton B. Stevenson. Used by permission

Abstract

This study investigates the prevalence and significance of forward-flank convergence boundaries (FFCBs) and left-flank convergence boundaries (LFCBs) in shaping the structure and intensity of supercells, using observational data from various field projects. Unlike previous research focusing on individual cases, this study examines a diverse range of cases to provide comprehensive insights into the relationship between these boundaries and supercell characteristics such as intensity, longevity, and tornadogenesis. By analyzing high-resolution surface data, the research addresses the frequency, location, and intensity of these boundaries, and their impact on pseudo vertical vorticity, pseudo convergence, and density gradients. A total of 228 boundary identifications are cataloged. Spatiotemporal filtering ensures these are unique boundary crossings, though multiple mesonets may have transected the same boundary at different positions. Due to storm-to-storm and temporal variability, spatial patterns in LFCB are difficult to discern, but a higher frequency of boundary occurrence is noted where the FFCB is often found. Pseudo-vertical vorticity is largest near and on the cool side of identified boundaries, highlighting the importance of baroclinicity and stretching on vorticity generation. Tornadic supercells consistently show larger pseudo-vertical vorticity and weaker density gradients across the boundary. Pseudo convergence is greatest near the mesocyclone, indicating enhanced potential for vertical vorticity stretching and low-level ascent. These findings underscore the critical role of FFCBs and LFCBs in supercell dynamics and the need for further research to understand these processes and their implications for tornadogenesis.

Advisor: Adam L. Houston