Jupiter's unearthly jets: a new turbulent model exhibiting statistical steadiness without large-scale dissipation

Abstract

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 (DI) 1-1/2-layer scenario and its supporting observational evidence, pointing toward deep, massive, zonally-symmetric zonal jets in the underlying dry-convective layer. The second is to improve the realism of the model stochastic forcing used to represent the effects of Jupiter's moist convection as far as possible within the 1-1/2-layer dynamics. The real moist convection should be strongest in the belts where the interface to the deep flow is highest and coldest, and should generate cyclones as well as anticyclones with the anticyclones systematically stronger. The new model forcing reflects these insights. Also, it acts quasifrictionally on large scales to produce statistically steady turbulent weather-layer regimes without any need for explicit large-scale dissipation, and with weather-layer jets that are approximately straight thanks to the influence of the deep jets, allowing shear stability despite nonmonotonic potential-vorticity gradients when the Rossby deformation lengthscale is not too large. Moderately strong forcing produces chaotic vortex dynamics and realistic belt-zone contrasts in the model's convective activity, through an eddy-induced sharpening and strengthening of the weather-layer jets relative to the deep jets, tilting the interface between them. Weak forcing, for which the only jet-sharpening mechanism is the passive (Kelvin) shearing of vortices (as in the "CE2" or "SSST" theories), produces unrealistic belt-zone contrasts.