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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
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