Date of Award

August 2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric Sciences

First Advisor

Jake P. Mulholland

Abstract

Supercell thunderstorms are a mesoscale phenomenon characterized by an intense rotating updraft (i.e., the “mesocyclone”) and disproportionately account for more severe weather reports compared to ordinary deep convection. No previous research that we are aware of has explicitly analyzed the role that cold pools – shallow regions of precipitation-cooled air near the surface – play in impacting supercell development, sustenance, and strength. This thesis aims to fill in the gaps to the fundamental questions surrounding what role cold pools play (if any) in permitting a supercell to develop and maintain itself, how cold pools affect the strength and structure of a supercell, and how important cold pools are in redirecting inflow air into a supercell updraft compared to what is being dynamically accelerated upward by the mesocyclone.

A suite of 16 simulations was conducted using an idealized numerical cloud model, Cloud Model 1 (CM1), in which half of the simulations permitted cold pool formation while the other half utilized a modified version of the Morrison two-moment microphysics scheme in which the cooling associated with evaporation of rain and melting of hail was turned off across the entire domain at model initialization, effectively prohibiting cold pool formation. Modifications were made to free tropospheric relative humidity, lifting condensation level height, and both low- and mid-level vertical wind shear of the base state environment to determine the robustness of our findings across different atmospheric regimes.

Our results suggest that cold pools play an important, although not necessary, role in tilting inflow air into a supercell updraft thus creating stronger low-level updraft rotation and strength, while also promoting increased storm translational velocity, low-level storm-relative inflow, and mid-level updraft size. These findings were generally consistent across different environments.

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