Dynamics Of The Cloud-Level Zonal Jets On Jupiter And Saturn: Lessons From A One-Layer Shallow-Water Model

Details Dynamics Of The Cloud-Level Zonal Jets On Jupiter And Saturn: Lessons From A One-Layer Shallow-Water Model Dynamics Of The Cloud-Level Zonal Jets On Jupiter And Saturn: Lessons From A One-Layer Shallow-Water Model

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.1116s&link_type=abstract

American Astronomical Society, DPS meeting #38, #11.16; Bulletin of the American Astronomical Society, Vol. 38, p.498

Astronomy and Astrophysics

Astronomy

Scientific paper

The question of what causes the numerous east-west zonal jets on the giant planets has remained a mystery since high-resolution Pioneer and Voyager images were returned in the 1970s. One hypothesis is that cloud-level turbulence undergoes an inverse energy cascade that reorganizes the energy into zonal jets. However, most studies of this phenomenon have been two-dimensional, which excludes the important influence of stratification--that is, finite deformation radius--on the flow. Furthermore, most such turbulence studies neglect the possible influence that deep jets underlying the weather layer may have on the weather-layer dynamics. Here, I present numerical simulations that address these two issues. I adopt the shallow-water equations, which are among the simplest atmospheric equations that include finite deformation radius, and include small-scale forcing to represent turbulence injected into the cloud layer. The simulations show that, when no deep jets are imposed, the deformation radius controls the behavior in the weather layer. At large deformation radii (> 4000 km), jets tend to dominate over vortices, but at small deformation radii (< 2000 km), vortices dominate over jets. This behavior results from the fact that, at small deformation radius, column stretching can suppress the beta effect necessary for jet production. However, the existence of multiple deep jets in the interior adds a "topographic" beta effect that allows jets to easily form in the weather layer even at small deformation radius. In such a case, the weather-layer jets violate the barotropic stability criterion but become neutrally stable with respect to Arnol'd's second stability criterion. The weather-layer jets are driven by convergence of eddy momentum into the jets, and a mean meridional flow develops that transports air from cyclonic regions (belts) to anticyclonic regions (zones). The implications of these results for the zonal jets and belt-zone structure on Jupiter and Saturn will be thoroughly discussed.

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