The initiation and mature structure of strongly forced squall-line thunderstorms
Jewett, Brian Ford
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https://hdl.handle.net/2142/20902
Description
Title
The initiation and mature structure of strongly forced squall-line thunderstorms
Author(s)
Jewett, Brian Ford
Issue Date
1996
Doctoral Committee Chair(s)
Wilhelmson, Robert B.
Department of Study
Atmospheric Science
Discipline
Atmospheric Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Atmospheric Science
Language
eng
Abstract
A great deal has been learned in the past 20 years from observations and numerical simulation of thunderstorms. The relationship between the character of isolated convection and the in-situ buoyancy and shear profiles has received considerable attention, and this work has yielded comparatively simple expressions which have been successfully applied to a surprisingly wide range of convective situations. Recent work has gone beyond isolated thunderstorms to squall lines.
Even with such understanding, questions remain regarding the role of mesoscale forcing in the convective setting. Intense convection and particularly long-lived severe convection is often associated with and preceded by lower-tropospheric lifting and distinct horizontal gradients in heat, moisture, wind or some combination. Despite this relationship, it is often held that the local vertical structure of buoyancy and shear will determine the convective regime. Clearly this is often true, remarkable given the variety of mesoscale phenomena (e.g., cold and warm fronts, drylines, and jet streaks) which accompany thunderstorms. Yet there are forms of convection which seem closely related to the phenomena which accompany them. Squall lines often form along cold fronts, isolated supercells are frequently found along the dryline and intense storms sometimes occur along warm fronts. Any relationship beyond simple initiation that exists between convection and mesoscale structures deserves a closer look, as it may help extend the shear and buoyancy relationships and lead to improved understanding and forecasts.
In this study the relationship between squall line thunderstorms and the environment is explored using numerical simulation. The mesoscale forcing here is the cold front, simulated and designed to produce the small-scale features and thermodynamic environments found near intense thunderstorms. Given such structures in the controlled environment of the cloud model, the attributes of the forcing may be altered or removed entirely to expose the role of the mesoscale on the initiation and long-term structure of squall line thunderstorms.
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