Statistics – Computation
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31a1229k&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P31A-1229
Statistics
Computation
[0343] Atmospheric Composition And Structure / Planetary Atmospheres
Scientific paper
1. Introduction In Jupiter's atmosphere, there are many large scale vortices, such as the Great Red Spot and White Ovals. Williams(1996) numerically examined the genesis and stability of large scale vortices using a three dimensional model. In many of his experiments, the emergence of waves due to an instability of unstable jets and gradual development into a coherent vortex resembling the Great Red Spot were reproduced. However, wind speed and temperature anomaly of the large scale vortex became weaker after a long time integration. The decay of the vortex might be caused by the variations of the zonal mean field from that of the initial condition. Therefore, we introduce forcing to maintain zonal mean fields, and examine possible sensitivities of the behavior of simulated vortices in the statistically steady state to the type and the intensity of the forcing. 2. Model and Setup We develop a three dimensional model based on the primitive equation model of the Boussinesq fluid. The computational domain covers 180 degrees in longitude with periodic boundary condition, from equator to -40 degrees in latitude, and 10000km vertically. The model atmosphere consists of a stably stratified 'weather' layer with 500km thickness and a deep neutral layer with 9500km thickness. We assume that the initial alternating jets are confined to the weather layer. The latitudinal structure of the temperature field is determined by assuming the thermal wind balance. These setups described so far follow those of the case A4 of Williams(1996). However, in this study, we introduce forcing to maintain the zonal mean field. We conduct 13 experiments with four types of forcing: 1. no forcing, 2. momentum forcing to damp the zonal mean winds to the initial, 3. thermal forcing to damp the zonal mean temperature to the initial, 4. both ( momentum and thermal ) forcing. Four values of damping time, which are 30, 100, 300, and 1000days, are used for the thermal and/or momentum forcing terms. Each numerical experiment is continued for 6000 days. 3. Results We find that the behavior of simulated vortices depend on the type and the damping time of forcing. Large scale coherent vortices are generated and maintained until the end of experiments only in cases with weak forcing. With strong forcing, such vortices are not maintained and the evolution of the model can be classified into two end members: many large scale vortices are generated but their lifetime is short in cases with momentum forcing, whereas no large scale appear in the long run with thermal forcing. As regards to zonal mean fields, in cases of momentum forcing alone with short damping time, the structure of temperature field change significantly. On the other hand, in cases of thermal forcing alone with short damping time, the structure of jets change significantly, esspecially barotropic component of jets are generated. These differences of zonal mean field in a steady state might cause the observed variety in the behavior of vortices. In the presentation, we will discuss more detail dynamic analysis.
Kato Reizo
Ko-Ichiro S.
Nakajima Kaoru
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