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

TL;DR

This study uses 3D simulations to explain why Jupiter and Saturn have different equatorial jet strengths and widths, linking these differences to the depth of their atmospheric zonal flows.

Contribution

It demonstrates that atmospheric depth, driven by convective eddy momentum flux, determines the strength and extent of equatorial jets on gas giants.

Findings

Saturn's deeper zonal flows lead to stronger, wider jets.

Atmospheric depth correlates with eddy momentum flux.

Results align with gravity measurements from spacecraft.

Abstract

Jupiter's equatorial eastward zonal flows reach wind velocities of ~100 m/s, 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.