The Characteristics of Numerically Simulated Supercell Storms Situated over Statically Stable Boundary Layers

Open Access
Author:
Nowotarski, Christopher
Graduate Program:
Meteorology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 05, 2010
Committee Members:
  • Jenni Evans, Thesis Advisor
  • Paul Markowski, Thesis Advisor
Keywords:
  • static-stability
  • tornadogenesis
  • elevated supercells
  • supercells
  • nocturnal inversion
Abstract:
Numerical simulations of supercell thunderstorms are used to assess changes in vertical motion and low-level rotation in environments with differing low-level static stability. Simulations are initialized in an idealized, horizontally homogeneous environment with a shallow stable layer that is representative of a nocturnal inversion or a mesoscale cold pool. The depth and temperature deficit of the imposed stable boundary layer, which together define the convective inhibition (CIN), are varied in a suite of simulations. When compared with a control simulation with little surface-based CIN, each supercell simulated in a stable boundary layer exhibits weaker low-level vertical vorticity and weaker low-level vertical velocity despite similar most unstable convective available potential energy (MUCAPE); in general, low-level vertical vorticity and vertical velocity decrease as CIN increases. It was found that while the presence of a stable boundary layer decreases low-level updraft strength, all supercells except those initiated over the most stable boundary layers had some updraft parcels with surface origins. Furthermore, the existence of a stable boundary layer does not prohibit downdraft parcels from reaching the surface, though decreased negative buoyancy decreases downdraft speed. Trajectory and circulation analyses indicate that the weaker rotation at low levels is a result of the decreased generation of circulation at low levels coupled with decreased convergence of the near-ground circulation by weaker storm updrafts in the stable-layer scenarios. These results also may suggest a reason why tornadogenesis is less likely to occur in elevated supercell thunderstorms.