2026-09-22T03:16:06Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/22205 2023-07-10 col_2142_5131 col_2142_8888 com_2142_5130 com_2142_8887 com_2142_234

Gardner, Chester S. Senft, Daniel Charles 2011-05-07T13:32:24Z 2011-05-07T13:32:24Z 10000-01-01 1991 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). Made available in DSpace on 2011-05-07T13:32:24Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9210985.pdf: 5540708 bytes, checksum: 167f3182db2ed496cfe1080e1739d29b (MD5) Previous issue date: 1991 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:56:02Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:26:10-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9210985 (UMI)AAI9210985 http://hdl.handle.net/2142/22205 eng Copyright 1991 Senft, Daniel Charles Geophysics Engineering, Electronics and Electrical Physics, Atmospheric Science Lidar studies of gravity waves in the mesopause region text Electrical and Computer Science Electrical Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.