Mesospheric Kelvin-Helmholtz instability

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Parker, Jay William

Contributors dc:contributor

• Bowhill, S.A.

• Engineering, Electronics and Electrical
• Physics, Atmospheric Science
• Physics, Fluid and Plasma

Statement dc:rights

• Copyright 1989 Parker, Jay William

Language dc:language

eng

Identifier

AAI8924915
(UMI)AAI8924915

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/21832