Depth Dependent Dynamics Explain the Equatorial Jet Difference Between Jupiter and Saturn

Jupiter's equatorial eastward zonal flows reach wind velocities of ∼100 m s−1, while on Saturn they are three times as strong and extend about twice as wide in latitude, despite the two planets being overall dynamically similar. Recent gravity measurements obtained by the Juno and Cassini spacecraft uncovered that the depth of zonal flows on Saturn is about three times greater than on Jupiter. Here we show, using 3D deep convection simulations, that the atmospheric depth is the determining factor controlling both the strength and latitudinal extent of the equatorial zonal flows, consistent with the measurements for both planets. We show that the atmospheric depth is proportional to the convectively driven eddy momentum flux, which controls the strength of the zonal flows. These results provide a mechanistic explanation for the observed differences in the equatorial regions of Jupiter and Saturn, and offer new understandings about the dynamics of gas giants beyond the Solar System. Plain Language Summary In this study, we investigate the strong eastward jet around the equator of Jupiter and Saturn. Despite the planets being similar, Saturn's winds are stronger and cover a wider area in latitude. Recent spacecraft measurements revealed that Saturn's winds go much deeper into its interior than Jupiter's. Using numerical simulations, we find that the depth of the atmosphere is crucial in determining the strength and width of these winds. We show that the depth is related to a specific turbulent flow, dictating the strength of the jets. These findings explain why Jupiter and Saturn have different equatorial zonal wind patterns and provide new insights into the behavior of giant planets outside the Solar System. Key Points Through 3D numerical simulations, we deduce that the flow depth of gas giants significantly influences their equatorial dynamics Equatorial flows are driven by eddy fluxes perpendicular to the axis of rotation, and these fluxes are proportionate to the flow depth The zonal flow depth of Jupiter and Saturn, inversely proportional to their 3:1 mass ratio, leads to the corresponding ratio in flow strength