Investigating Barotropic Zonal Flow in Jupiter's Deep Atmosphere using Juno Gravitational Data

TL;DR

This study models Jupiter's deep atmospheric zonal flow as barotropic and uses Juno gravitational data to show that observed surface winds extending to about 1000 km depth can explain most of the measured gravitational harmonics.

Contribution

It introduces a barotropic flow model to interpret Juno gravitational data, exploring the depth and structure of Jupiter's zonal winds and their gravitational signatures.

Findings

Most antisymmetric gravitational signals explained by ~1000 km deep flows.

Observed winds between 20.9°S and 26.4°N extend to depths of ~1000 km.

Juno odd zonal harmonics fully explained by these deep barotropic flows.

Abstract

The high-precision Juno gravitational measurements allow us to infer the structure of Jupiter's deep atmospheric zonal flow. Since this inference is nonunique, it is important to explore the space of possible solutions. In this paper, we consider a model in which Jupiter's deep atmospheric zonal flow is barotropic, or invariant along the direction of the rotation axis, until it is truncated at depth by some dynamical process (e.g., Reynolds stress, Lorentz or viscous force). We calculate the density perturbation produced by the $z$-invariant part of the flow using the thermal wind equation and compare the associated odd zonal gravitational harmonics ($J_{3}$, $J_{5}$, $J_{7}$, $J_{9}$) to the Juno-derived values. Most of the antisymmetric gravitational signal measured by Juno can be explained by extending observed winds between $20.9^{\circ}\rm{S}-26.4^{\circ}\rm{N}$ to depths of $\sim 1000$ km. Because the small-scale features of the mid/high latitude zonal flow may not persist to depth, we allow the zonal flow in this region to differ from the observed surface winds. We find that the Juno odd zonal gravitational harmonics can be fully explained by $\sim 1000$ km deep barotropic zonal flows involving the observed winds between $20.9^{\circ}\rm{S}-26.4^{\circ}$N and a few broad mid/high latitude jets.