Citation
Achterberg, Richard Karl (1992) Numerical Simulation of Baroclinic Jovian Vortices. Dissertation (Ph.D.), California Institute of Technology. https://resolver.caltech.edu/CaltechTHESIS:09262011111706613
Abstract
This thesis consists of two papers on the dynamics of Jovian planet atmospheres. The first paper discusses the uses of a normalmode expansion in the vertical for modeling the dynamics of Jupiter's atmosphere. The second paper uses a nonlinear numerical model based on the normalmode expansion of the first paper to study the dynamics of baroclinic vortices. The abstracts for the two papers are reproduced below.
Paper 1:
We propose a nonlinear, quasigeostrophic, baroclinic model of Jovian atmospheric dynamics, in which vertical variations of velocity are represented by a truncated sum over a complete set of orthogonal functions obtained by a separation of variables of the linearized quasigeostrophic potential vorticity equation. A set of equations for the time variation of the mode amplitudes in the nonlinear case is then derived. We show that for a planet with a neutrally stable, fluid interior instead of a solid lower boundary, the barotropic mode represents motions in the interior, and is not affected by the baroclinic modes. One consequence of this is that a normal mode model with one baroclinic mode is dynamically equivalent to a one layer model with solid lower topography. We also show that for motions in Jupiter's cloudy lower troposphere, the stratosphere behaves nearly as a rigid lid, so that the normalmode model is applicable to Jupiter. We test the accuracy of the normalmode model for Jupiter using two simple problems: forced, vertically propagating Rossby waves, using two and three baroclinic modes, and baroclinic instability, using two baroclinic modes. We find that the normalmode model provides qualitatively correct results, even with only a very limited number of vertical degrees of freedom.
Paper 2:
We examine the evolution of baroclinic vortices in a time dependent, nonlinear numerical model of a Jovian atmosphere. The model uses a normalmode expansion in the vertical, using the barotropic and first two baroclinic modes (Achterberg and Ingersoll 1989). Our results for the stability of baroclinic vortices on an ƒplane in the absence of a mean zonal flow are consistent with previous results in the literature, although the presence of the deep fluid interior on the Jovian planets appears to shift the stability boundaries to smaller length scales. The presence of a mean zonal shear flow acts to stabilize vortices against instability, significantly modifies the finite amplitude form of baroclinic instabilities, and combined with internal barotropic instability (Gent and McWilliams 1986) produces periodic oscillations in the latitude and longitude of the vortex as observed at the level of the cloud tops. This instability may explain some, but not all, observations of longitudinal oscillations of vortices on the outer planets. Oscillations in aspect ratio and orientation of stable elliptical vortices in a zonal shear flow are observed in this baroclinic model, as in simpler twodimensional models (Kida 1981). The meridional propagation and decay of vortices on a βplane is inhibited by the presence of a mean zonal flow. The direction of propagation of a vortex relative to the mean zonal flow depends upon the sign of the meridional potential vorticity gradient; combined with observations of vortex drift rates, this may provide a constraint on model assumption for the flow in the deep interior of Jupiter.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Subject Keywords:  Planetary Science and Astronomy 
Degree Grantor:  California Institute of Technology 
Division:  Geological and Planetary Sciences 
Major Option:  Planetary Sciences Astronomy 
Thesis Availability:  Public (worldwide access) 
Research Advisor(s): 

Group:  Astronomy Department 
Thesis Committee: 

Defense Date:  3 October 1991 
Record Number:  CaltechTHESIS:09262011111706613 
Persistent URL:  https://resolver.caltech.edu/CaltechTHESIS:09262011111706613 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  6688 
Collection:  CaltechTHESIS 
Deposited By:  John Wade 
Deposited On:  26 Sep 2011 18:42 
Last Modified:  02 Dec 2020 02:07 
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