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

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 study, 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 degrees S and 26.4 degrees N to depths of similar to 1000 km. Because the small-scale features of the midlatitude/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 similar to 1000 km deep barotropic zonal flows involving the observed winds between 20.9 degrees S-26.4 degrees N and a few broad midlatitude/high-latitude jets. Plain Language Summary One of Jupiter's most recognizable features is its surface pattern of zonal (east-west) winds. Since large-scale flows are expected to produce a signature in the planet's gravitational field, we can use the Juno gravitational data to test different zonal flow models. In this paper, we test a model in which the zonal flow extends into the interior along the direction of the planetary rotation axis without decay until it is truncated at depth by some dynamical process. The model remains agnostic on the exact truncation mechanism, although possibilities include interaction with a stably stratified layer or the magnetic field. We find that most of the dynamical gravitational field measured by Juno can be explained by extending the observed surface winds between 20.9 degrees S-26.4 degrees N to depths of similar to 1,000 km. The Juno data can be fully explained when these flows are combined with a few broad midlatitude/high-latitude jets with peak amplitudes of about 10 m s(-1).