Basic dynamics of low-frequency variability and the storm tracks
Cai, Ming
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Permalink
https://hdl.handle.net/2142/22153
Description
Title
Basic dynamics of low-frequency variability and the storm tracks
Author(s)
Cai, Ming
Issue Date
1990
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 first part of this thesis is a study of the dynamics of storm tracks from the perspective of local instability of a class of zonally inhomogeneous basic jet streams. An unstable local mode consists of a group of dominant waves which jointly give rise to a maximum local energy downstream of the jet core. Its growth rate diminishes very rapidly as the constant part of the basic zonal wind is increased, but is not sensitive to the zonally averaged part of the shear flow. The non-modal analysis shows the excitation of a local mode within a few days from an initially isolated disturbance depends strongly on the initial position relative to the jet core but less strongly on the initial configuration of the isolated disturbance. A complete set of local energy equations has been formulated to reveal the nature of the various physical mechanisms of the instability of a zonally inhomogeneous basic flow. The energy redistribution processes are comparable in importance to the energy generation processes themselves. They are found to counteract one another to a great extent resulting in a net downstream intensification of a disturbance.
The second part considers the problem of the mutual dependence of planetary and synoptic scale waves in the context of a high resolution, zonally forced, dissipative, two-layer quasi-geostrophic channel model. We have specifically examined the dynamical properties of the equilibrated flow in a 6000-day numerical experiment with a realistic forcing parameter. The wave field in the equilibrated state is dominated by the planetary scale wave with wavenumber (m,n) = (2,2) and the synoptic scale waves (m,n) = (4,1) and (5,1). The modified zonal flow together with the internally forced planetary scale wave may be viewed as a zonally inhomogeneous background flow upon which the synoptic scale eddies grow preferentially downstream of the planetary scale jet streams. The synoptic eddies in turn sustain the planetary scale wave barotropically at the expense of the potential energy created by the radiative differential heating.
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