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Title:Mesospheric Kelvin-Helmholtz instability
Author(s):Parker, Jay William
Doctoral Committee Chair(s):Bowhill, S.A.
Department / Program:Electrical and Computer Engineering
Discipline:Electrical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Electronics and Electrical
Physics, Atmospheric Science
Physics, Fluid and Plasma
Abstract:This work examines the Kelvin-Helmholtz instability, comparing features extracted from a numerical fully nonlinear model to radar and rocket measurements of free electron density and neutral motions in the mesosphere. Previous models of shear instability are reviewed, and relevant mesospheric observations are summarized. The contour dynamics numerical model is employed, which utilizes the boundary of a region of constant vorticity to compute the velocity field. The velocity field is used to transport initial contours representing the vorticity boundary and lines of constant scalar. The nonlinear instability is found to produce thin regions of large scalar gradient which wind about a developing array of rotating elliptical vortices. Portions of the large-gradient regions are also transported downstream to form a laminated region of alternating gradient between the vortices. A first-order correction for the effects of diffusion in the large-gradient regions is presented, and used to estimate the initial shear responsible for irregularities in electron density observed by a rocket probe. A technique is presented which reconstructs the broadband mesospheric electron density profile from two filtered rocket probe signals. A correspondence is demonstrated between small-scale structures in this profile near an altitude of 75 km, and cross sections of the model scalar. The vertical component of the perturbation velocity field of the instability is extracted from the model. Vertical profiles of the amplitude and phase of the horizontal first harmonic of the vertical velocity are shown to agree qualitatively with radar observations and previous linear models in the early stages of the instability, but qualities found in the later amplitude and phase model profiles have not yet been observed.
Issue Date:1989
Rights Information:Copyright 1989 Parker, Jay William
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI8924915
OCLC Identifier:(UMI)AAI8924915

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