Origin, Maintenance and Fine-Scale Structure of 14-15 February 1992 Mesoscale Gravity Wave Observed During Storm-Fest
Yang, MuQun
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https://hdl.handle.net/2142/85986
Description
Title
Origin, Maintenance and Fine-Scale Structure of 14-15 February 1992 Mesoscale Gravity Wave Observed During Storm-Fest
Author(s)
Yang, MuQun
Issue Date
1999
Doctoral Committee Chair(s)
Rauber, Robert M.
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
Language
eng
Abstract
The gravity wave was generated behind the leading edge of an advancing dry surge moving over a warm frontal inversion. The dry surge, which had the characteristics of density current, originated as a foehn-like downslope flow over the Rocky Mountains of southern Colorado and New Mexico. The advancing dry surge provided a continuous energy source for both the mesoscale gravity wave and convection. Internal circulations within the dry surge created the mesoscale gravity wave while lifting of air ahead of the dry surge created a line of convection. There was no direct relationship between the convection and the mesoscale gravity wave in the sense that neither forced the other. Both were generated and maintained by the advancing dry surge. Deceleration within the dry surge led to a branched circulation within the flow, with the descending branch depressing the height of the warm frontal inversion creating the wave, and the ascending branch creating the dry surge head. Pressure and virtual potential temperature perturbations were generated by the advancing dry surge and associated convection. Strong horizontal perturbation pressure gradients were associated with both the abrupt deceleration of air near the leading edge of the dry surge and with the divergent flow at the top of the convective updraft. The virtual potential temperature perturbation was associated with the vertical gradient of pressure perturbation because the convection was weak. In the second phase, in central-eastern Missouri, the wave disturbance decoupled from, and moved ahead of the dry surge. Surface pressure and wind measurements suggest that the disturbance was a bore. The bore propagated into a region where wave-ducting was effective, allowing it to maintain its structure over a long distance.
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