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https://hdl.handle.net/2142/20248
Description
Title
Evolution of atmospheric baroclinic waves
Author(s)
Chou, Han-Yun
Issue Date
1989
Doctoral Committee Chair(s)
Mak, Mankin
Department of Study
Atmospheric Sciences
Discipline
Atmospheric Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Atmospheric Science
Language
eng
Abstract
The evolution of atmospheric baroclinic waves is investigated by a six-layer forced dissipative quasi-geostrophic $\beta$-plane channel model. In the control run, the model has: (i) a realistic zonal thermal forcing, (ii) a surface Ekman layer, a Newtonian cooling and an interior biharmonic friction as the dissipation and (iii) an initial state consisting of a weak but general wave field superimposed on a jet-like zonal mean flow. The whole evolution of the baroclinic waves can be divided into three periods; namely, the baroclinically growing period in which the synoptic waves grow exponentially, the transition period in which the synoptic waves decay and the planetary waves grow, and the equilibration period in which the planetary waves become dominant. The synoptic waves stop growing exponentially due to the wave-wave interaction as well as the barotropic decay as pointed out by Simmons and Hoskins (1978). The planetary waves are forced by the synoptic waves through the nonlinear cascade process. The energy spectra show a $\lambda\sp{-3}$ distribution in the region of high total wavenumber ($\lambda$) and a $\lambda\sp{-5/3}$ distribution in the low wavenumber region.
In the sensitivity experiments, it is found that the spectral composition in the equilibrated state is not qualitatively dependent upon the meridional structure in the zonal thermal forcing. But when the latter is absent, the wave field is substantially stronger. A jet zonal mean flow is generated in the center of the domain, although it is initially uniform. As a potential vorticity forcing is applied, it gives rise to a wave field dominated by the (5, 1) wave, which has the same horizontal scale as the most unstable mode according to the linear theory, instead of the long waves in the control run and the other studies. When the initial condition consists of only a single synoptic scale wave, no planetary waves can be excited. Finally, the two-layer model results are qualitatively similar to those of the six-layer model although it takes longer to reach an equilibrated state than in the six-layer model.
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