Earth and Atmospheric Sciences, Department of


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A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree Master of Science Major: Geosciences Under the Supervision of Professor Adam L. Houston Lincoln, Nebraska May, 2010 Copyright 2010 Jennifer M Laflin


It is theorized that supercell thunderstorms account for the majority of significantly severe convective weather which occurs in the United States, and as a result, it is necessary that the mechanisms which tend to produce supercells are recognized and investigated. Airmass boundaries have been identified as a preferred location for supercell development due to the enhanced horizontal vorticity and forced ascent that are found along the boundary. This study examines the specific influence of a preexisting airmass boundary on supercell development through a set of idealized simulations. These simulations are based on a supercell which formed along an outflow boundary in the panhandle of Texas on 25 May 1999, and involve both homogeneous environments from the warm and cool sides of the boundary, as well as a representation of the actual environment with a boundary present. Detailed analyses of these simulations are then performed to determine the specific influence of the preexisting airmass boundary on supercell formation and morphology. It was found that the airmass boundary has three main impacts on the simulated storm: 1) enhancement of the updraft by forced ascent along the boundary, which allows a stronger right-splitting storm to develop, 2) production of a gust front through a combination of storm outflow and the cool airmass, which allows the storm to transition away from precipitation and continually draw in warm air, and 3) provision of enhanced horizontal vorticity that supports the development and maintenance of a low-level mesocyclone.