Numerical Simulations of a Midlatitude Squall Line
Fovell, Robert Gerard
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https://hdl.handle.net/2142/70926
Description
Title
Numerical Simulations of a Midlatitude Squall Line
Author(s)
Fovell, Robert Gerard
Issue Date
1988
Doctoral Committee Chair(s)
Ogura, Yoshimitsu,
Department of Study
Atmospheric Sciences
Discipline
Atmospheric Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Atmospheric Science
Abstract
A two-dimensional, nonhydrostatic cloud model was used in attempts to numerically replicate the observed structure of a typical midlatitude squall line. The basic simulations described in this report were made using common temperature and moisture profiles in the vertical, and emphasis was placed on varying the microphysics and the vertical wind shear. The temperature and moisture profiles chosen were adapted from the environmental conditions which were present prior to the development of the 22 May 1976 Oklahoma squall line and were typical of environments which supported severe springtime convection in that area.
The model storms described herein were all similar in that they organized themselves into long-lasting mature states marked by behavior which was more or less multicellular, depending on the strength of the wind shear. Each storm persisted through the production of new cells at the leading edge of the storm, over the storm's gust front. This production proceeded in a quite regular manner in virtually every case, although specific details such as the length and composition of the repeat cycle and the total precipitation produced were sensitive to the microphysics and the strength of the vertical wind shear. However, each of the model storms appear to have achieved a very long-lasting, quasi-equilibrium state; the only major exceptions to this were among the smallest shear cases where random influences were more apparent.
The incorporation of ice processes into the microphysics resulted in the production of more horizontally extensive storms which possessed estimated radar reflectivity fields which were more realistic in appearance. Increasing the vertical wind shear had the effect of producing narrower, more intense model storms which propagated more quickly. The response of the model convection to increasing wind shear was considered within the context of recent ideas concerning the vorticity dynamics of actual squall lines. Dynamically, however, all of the model storms were quite similar as there were general features which were common to all of the runs.
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