Linear Dynamic Pressure Explains the Persistence of Supercell Rear Flank Downdrafts
Open Access
Author:
Brandt, Samuel
Graduate Program:
Meteorology and Atmospheric Science
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 10, 2024
Committee Members:
John M Peters, Thesis Advisor/Co-Advisor Matthew Robert Kumjian, Committee Member Jerry Harrington, Professor in Charge/Director of Graduate Studies Jerry Y Harrington, Committee Member
Supercells are perhaps the most organized form of thunderstorm, with structure that persists over relatively long periods of time. Part of this persistent structure is a feature referred to as the “rear flank downdraft” (RFD). There is a bevy of prior research on short duration downdraft surges in this region, but ample room for a dynamic understanding of the persistence of RFDs exists. Bulk analysis of numerous trajectories within simulations of supercells across environments with varied shear and lifted condensation level (LCL) shows that reductions in the vertical perturbation pressure gradient acceleration (VPPGA) are primarily responsible for the downward acceleration of near-surface downdrafts in the RFD region. Time averaged and updraft centered composites suggest that linear dynamic VPPGA resulting from interactions between environmental vertical wind shear and the low-level supercell updraft explain the persistence of the RFD region. A technique is presented to compare the potential for linearly forced supercell RFD between environments using a vertical wind profile.
