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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
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
Rights Information:Copyright 1991 Senft, Daniel Charles
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9210985
OCLC Identifier:(UMI)AAI9210985

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