The role of eddy fluxes in the response of the atmosphere to tropical thermal forcing
Wu, Huey-Tzu
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https://hdl.handle.net/2142/19097
Description
Title
The role of eddy fluxes in the response of the atmosphere to tropical thermal forcing
Author(s)
Wu, Huey-Tzu
Issue Date
1991
Doctoral Committee Chair(s)
Anderson, John F.
Department of Study
Atmospheric Science
Discipline
Atmospheric Science
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 applicability of linear models in studying the observed stationary waves is considered. In particular, the time-mean effects of eddy fluxes on the response of the atmosphere to tropical thermal forcing are examined by using a time-dependent, nonlinear, global, baroclinic primitive equation model. It is shown that the lack of proper phase and spatial scale of previous linear simulations can be explained to a large degree by the effects of transient eddy fluxes.
In this study, the nonlinear anomaly response to an isolated region of thermal anomalies is defined as the difference between the perturbation simulation and the basic solution of our forced model. Results indicate that the nonlinear response is a superposition and interaction of two components: a quasi-stationary mode which can be resolved by linear dynamics and a zonally propagating mode which owes its existence to baroclinic instability.
Effects of basic state advection by standing eddies, which were included in the linear studies, are responsible for over half the anomaly response amplitude. As a result, the linear dynamics can account for several gross features of the anomaly response. These include the dominance of zonal wavenumbers 1 and 2 in high latitudes, the equivalent barotropic nature of the remote response, and the baroclinic nature of the near source response.
Effects of eddy fluxes by nonlinear standing eddies are very small and do not show a clear relationship to the anomaly response. On the other hand, the transient eddies show a substantial impact on the anomaly response, especially for the mid-latitude lower troposphere. Specifically, this study suggests that the transient eddy flux mechanism is responsible for the large zonal scale of the anomaly response. The transient eddies also act to lead the anomaly response, and hence have a significant influence on its phase. In addition, the transient eddy effects are not dissipative, but rather enhance somewhat the amplitude of the anomaly response, especially for zonal wavenumbers 1 and 2 in mid and high latitudes. This suggests that it is unjustified to represent the transient eddy effects by a simple damping term in the linear models.
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