An Idealized Modeling Study of the Nontornadic and Tornadic Supercells Intercepted by VORTEX2 on 10 June 2010
Open Access
- Author:
- Klees, Alicia Marie
- Graduate Program:
- Meteorology and Atmospheric Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 12, 2020
- Committee Members:
- Yvette Pamela Richardson, Dissertation Advisor/Co-Advisor
Yvette Pamela Richardson, Committee Chair/Co-Chair
Paul Markowski, Committee Member
David Jonathan Stensrud, Committee Member
Andrew Mark Carleton, Outside Member
Glen Romine, Special Member
David Jonathan Stensrud, Program Head/Chair - Keywords:
- tornadoes
supercells
storm environments
low-level shear
numerical modeling
dynamic lifting - Abstract:
- Why do only a relatively small fraction of supercells produce tornadoes? One process that is thought to make tornado production more favorable in a supercell thunderstorm is increasing low-level vertical wind shear in the storm environment, as this leads to increased dynamic lifting and potentially greater intensification of near-surface vorticity; this process is the focus of this study. Idealized CM1 simulations of a nontornadic (NT) supercell and a tornadic (T) supercell, loosely based on the supercells observed by the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) on 10 June 2010 are analyzed, along with an idealized simulation of a NT supercell that experiences increasing low-level shear. The time from initiation at which the shear begins to increase in the NT supercell's environment is varied from 30 min to 120 min. Consistent with theory and past studies, the storms that develop in an environment with larger low-level shear, or with low-level shear that increases over time, tend to have a stronger mesocyclone, stronger updraft and dynamic lifting, a lower-based mesocyclone, a greater extent of horizontal near-surface convergence, and some stronger near-surface vortices than the nontornadic storm, which develops in an environment with weaker low-level shear. A storm's response to increasing shear is found to be sensitive to the timing of the shear increase; the earlier the shear increase begins, the more favorably the storm evolves. The storms that experience increasing shear, while different from each other in some ways, do produce near-surface vortices with similar characteristics. Perhaps most interestingly, even one of the sub-optimal storms, having a far weaker updraft and mesocyclone at many times, is still able to produce a strong near-surface vortex. Additionally, even when the shear increase begins as early as 30 min after initiation, the resulting storm never reaches the strength of the T storm, or is as prolific a producer of strong near-surface vortices.