Abstract
We test the hypothesis that the atmospheric circulations of Jupiter are a manifestation of large-scale convective instability brought about primarily by the presence of an internal heat source. This is done by examining the nature of convection in an unstable rotating atmosphere through numerical integration of the Boussinesq equations. The general properties of convection are obtained from solutions with laboratory-scale parameters while particular Jovian characteristics are studied through calculations with planetary-scale parameters.
In the Jupiter calculations, physical and theoretical constraints on parametric freedom produce a desirably under-determined system in which there remain more observational criteria to be explained than free parameters to manipulate.
The solutions indicate that a tropical westerly jet can be produced by an axisymmetric flow provided that the atmosphere is relatively shallow (d<500 km). A strong equatorial westerly flow can occur provided that there is a strong diffusion of the tropical jet. The strength of such a diffusion is of a magnitude that suggests that it can only realistically be brought about by large-scale non-axisymmetric disturbances. The axisymmetry of the convective rolls, i.e., their longitudinal stability, is controlled by the latitudinal variation of Ω cosθ. This differential rotation suppresses the organization of large-scale convective motion poleward of 45° while toward the equator such motions can set in strongly.
The banded structure and zonal velocity field of the most realistic theoretical solution resemble the observed, having five zones (ω>O) and four belts (ω<O) each with its characteristic differential zonal motion. The square-shaped form of the mean vertical velocity variation with latitude produces sharply bounded zones of uniform intensity.
Calculations to test the stability of the axisymmetric flow to longitudinal perturbations indicate that ovals and streaks are the natural form of the disturbance elements.
