http://arxiv.org/abs/1412.4684
A longstanding mystery about Jupiter has been the straightness and steadiness of its weather-layer jets, quite unlike terrestrial strong jets with their characteristic unsteadiness and long-wavelength meandering. The problem is addressed in two steps. The first is to take seriously the classic Dowling-Ingersoll $1 {-2pt}\frac{1}{2}$-layer scenario and its supporting observational evidence. The evidence implies the existence of deep, massive, zonally-symmetric zonal jets in the underlying dry-convective layer. There is then the possibility of straight, stable weather-layer jets with the deep jets acting as guide-rails. Stability is possible even with nonmonotonic weather-layer potential-vorticity gradients. The second step is to improve the realism of the small-scale stochastic forcing used to represent Jupiter’s moist convection, as far as possible within the $1 {-2pt}\frac{1}{2}$-layer dynamics. The real, three-dimensional moist convection should be strongest in the belts where the interface to the deep flow is highest and coldest. It is likely, moreover, to generate cyclones as well as anticyclones but with the anticyclones systematically stronger. Such forcing can act quasifrictionally on large scales, and thus produce statistically steady turbulent weather-layer regimes without artificial large-scale friction. Forcing strengths sufficient to produce chaotic vortex dynamics can also produce realistic belt-zone contrasts in the model’s moist-convective activity, through a tilting of the interface by eddy-induced sharpening and strengthening of the weather-layer jets relative to the deep jets. Weaker forcing for which the only jet-sharpening mechanism is the passive (Kelvin) shearing of vortices, the so-called “CE2” or “SSST” or “zonostrophic instability” mechanism, produces unrealistic belt-zone structures.
S. Thomson and M. McIntyre
Tue, 16 Dec 14
24/78
Comments: Submitted to JAS. 18 pages, 13 figures
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