Theory and Observations of Horizontal and Vertical Structure of Gravity Wave Perturbations in the Middle Atmosphere
Hostetler, Chris Alan
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https://hdl.handle.net/2142/72003
Description
Title
Theory and Observations of Horizontal and Vertical Structure of Gravity Wave Perturbations in the Middle Atmosphere
Author(s)
Hostetler, Chris Alan
Issue Date
1993
Doctoral Committee Chair(s)
Gardner, Chester S.
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geophysics
Physics, Atmospheric Science
Abstract
Gravity wave models for the horizontal wave number spectra of atmospheric velocity and density fluctuations are derived by assuming that both saturated and unsaturated waves obey the polarization and dispersion relations and that the joint $(m{,}\omega)$ spectrum is separable. The models show that the joint $(k, l, m)$ and $(k, l, \omega$) spectra are not separable. The one-dimensional horizontal wave number spectra models are consistent with existing observations of horizontal wave number spectra in the lower stratosphere and upper mesosphere. The gravity wave models are used to analyze the effects of Doppler shifting caused by the mean wind field on the separability of gravity wave spectra. If the intrinsic joint $(m,\omega)$ spectrum is separable, Doppler effects associated with even small mean winds will destroy separability of the observed joint $(m,\omega\sb{\rm o})$ spectrum, particularly at high vertical wave numbers. Vertical and horizontal wave number spectra of density perturbations in the upper stratosphere (25-40 km) and the upper mesosphere ($\sim$80-105 km) measured during the ALOHA-90 campaign are presented. The spectra were inferred from $\sim$45 h of airborne Na/Rayleigh lidar observations in the vicinity of Hawaii. Density variances, vertical shear variances, Richardson's numbers, characteristic vertical and horizontal wave numbers, and power law slopes of the vertical and horizontal wave number spectra are computed and discussed. The observed m-spectra contradict the predictions of the linear instability theory of Dewan and Good (1986) and the scale-dependent diffusive filtering theory of Gardner (1993) and appear to be compatible with the Doppler spreading theory of Hines (1991, 1993), the scale-dependent diffusion theory of Weinstock (1990), the scale-independent diffusive filtering theory of Gardner (1993), and the similitude model of Dewan (1991). In the stratosphere, the m-spectra exhibit significant energy at low wave numbers less than the values expected for $m\sb*.$ The source of this energy is believed to be geostrophic adjustment of the jet stream.
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