Idealized modeling of the role of stability and shear on mesoscale gravity wave evolution

Pitcel, Michelle M.

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https://hdl.handle.net/2142/16155 Copy

Description

Title

Idealized modeling of the role of stability and shear on mesoscale gravity wave evolution

Author(s)

Pitcel, Michelle M.

Issue Date

2010-05-19T18:39:14Z

Director of Research (if dissertation) or Advisor (if thesis)

• Rauber, Robert M.
• Jewett, Brian F.
• McFarquhar, Greg M.

Department of Study

Atmospheric Sciences

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Mesoscale gravity waves (MGW)
• Meteorology
• Mesoscale
• Gravity wave
• Severe weather
• Weather Research and Forecast Model (WRF)

Abstract

Mesoscale Gravity Waves (MGWs) are large pressure perturbations that form in the presence of a stable layer at the surface either behind Mesoscale Convective Systems (MCSs) in summer or over warm frontal surfaces behind elevated convection in winter. MGWs are associated with damaging winds, moderate to heavy precipitation, and occasional heat bursts at the surface. The forcing mechanism for MGWs in this study is hypothesized to be evaporative cooling occurring behind a convective line. This evaporatively-cooled air generates a downdraft that then depresses the surface-based stable layer and causes pressure decreases, strong wind speeds and MGW genesis. Using the Weather Research and Forecast Model (WRF) version 3.0, evaporative cooling is simulated using an imposed cold thermal. Sensitivity studies examine the response of MGW structure to different thermal and shear profiles where the strength and depth of the inversion are varied, as well as the amount of wind shear. MGWs are characterized in terms of response variables, such as wind speed perturbations (U'), temperature perturbations (T'), pressure perturbations (P'), potential temperature perturbations (Θ'), and the correlation coefficient (R) between U' and P'. Regime Diagrams portray the response of MGW to the above variables in order to better understand the formation, causes, and intensity of MGWs. The results of this study indicate that shallow, weak surface layers coupled with deep, neutral layers above favor the formation of waves of elevation. Conversely, deep strong surface layers coupled with deep, neutral layers above favor the formation of waves of depression. This is also the type of atmospheric setup that tends to produce substantial surface heating at the surface.

Graduation Semester

2010-5

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http://hdl.handle.net/2142/16155

Copyright and License Information

Copyright 2010 Michelle M. Pitcel

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