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Title: | Lidar studies of gravity waves in the mesopause region |
Author(s): | Senft, Daniel Charles |
Doctoral Committee Chair(s): | Gardner, Chester S. |
Department / Program: | Electrical and Computer Science |
Discipline: | Electrical Engineering |
Degree Granting Institution: | University of Illinois at Urbana-Champaign |
Degree: | Ph.D. |
Genre: | Dissertation |
Subject(s): | Geophysics
Engineering, Electronics and Electrical Physics, Atmospheric Science |
Abstract: | Nightly and seasonal variations in gravity wave activity in the mesopause region are examined by analyzing 60 nights of Na lidar observations obtained during a five-year period at Urbana, Illinois. The lidar data were used to calculate atmospheric density perturbations and their spectra. The atmospheric density variances, density vertical shear variances, vertical wind variances, $\omega$-spectra magnitudes, and m-spectra magnitudes all exhibit considerable nightly variability as well as strong annual and semi-annual variations with the largest values in summer. The annual mean value of the rms density perturbations is 5.6%, with a mid-summer value that is 2 to 3 times larger. The Richardson number for the wave field varies between 1/2 and 2 for most of the year, although Ri sometimes falls well below 1/4 during the summer. The $\omega$-spectra exhibit power-law shapes with slopes varying between $-$1.28 and $-$2.45, with an annual mean of $-$1.82. The m-spectra also exhibit power-law shapes with slopes varying between $-$2.20, and $-$3.55, with a mean of $-$2.90. The magnitudes of both the $\omega$-spectra and m-spectra vary by more than a factor of 10 throughout the year, with the largest values in summer. The variability of the m-spectra slopes and magnitudes is not consistent with linear instability theory and the concept of a universal vertical wave number spectrum. The characteristic periods (T$\sb\* = 2\pi/\omega\sb\*)$ vary between 3 and 50 h with an annual mean of 9.7 h. The characteristic vertical wavelengths ($\lambda\sb\*$ = 2$\pi$/m$\sb\*)$ vary between 8.9 and 27 km with an annual mean of 14.1 km. The rms bandwidths of the wave field have mean values of $\bar\omega\sb{\rm rms}$ = 2$\pi$/(44 min) and $\bar{\rm m}\sb{\rm rms}$ = 2$\pi$/(6.2 km). |
Issue Date: | 1991 |
Type: | Text |
Language: | English |
URI: | http://hdl.handle.net/2142/22205 |
Rights Information: | Copyright 1991 Senft, Daniel Charles |
Date Available in IDEALS: | 2011-05-07 |
Identifier in Online Catalog: | AAI9210985 |
OCLC Identifier: | (UMI)AAI9210985 |
This item appears in the following Collection(s)
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Dissertations and Theses - Electrical and Computer Engineering
Dissertations and Theses in Electrical and Computer Engineering -
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois