Jason Naylor

Date of Award

January 2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric Sciences

First Advisor

Matthew S. Gilmore

Abstract

Simulations were performed in an idealized cloud model to study the processes responsible for tornadogenesis and tornadogenesis failure. The simulations were initialized with supercell proximity soundings taken from the Rapid Update Cycle (RUC) model. Because of the large number of simulations performed, several objective techniques were developed and tested to assist in the simulations--including automated supercell and tornado detection. In addition, the vast majority of the RUC soundings contained capping inversions, and thus the traditional `warm bubble' convective initiation technique was unsuccessful. A new sustained convective initiation technique was tested to determine which configuration produced the strongest, longest-lived supercells.

Twenty-one tornadic simulations were examined. It was found that 0-3 km storm relative environmental helicity was the best predictor of the intensity (i.e. maximum pressure drop) and duration of the simulated tornadoes. A trajectory analysis found that vertical vorticity was generated in rising parcels as they ascended towards the tornado, and also by parcels that descended from aloft. However, large positive vertical vorticity was only produced after the parcels reached the surface. The most striking difference between the tornadic and nontornadic simulations was that the tornadic simulations produced more negative vertical vorticity in descending parcels, and that the parcels that entered the low-level circulation rose to higher altitudes than the parcels in the nontornadic simulations.

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