Determining the Depth of Jupiter's Zonal Flows Using Gravity Measurements: Results from Juno's First Year Orbiting Jupiter

The observed cloud-level wind of Jupiter's atmosphere exhibits strong east-west jet streams reaching over 100 m/s. The depth of these jets has been a key unknown for understanding Jupiter's atmospheric dynamics. Theories range between shallow jets confined to the observable cloud-level to deep jets that are a surface manifestation of deep convective cylinders extending deep into the planet's interior. Since July 2016 the Juno spacecraft has been orbiting Jupiter, performing close flybys of the planet every 53 days. The eccentric orbit allows performing high precision gravity measurements of the planet, which can be used to determine the depth of the atmospheric flows and vertical structure of the cloud-level winds. Based on results from Juno's first six flybys, we discuss the Juno gravity experiment and show results for the depth and vertical structure of the atmospheric flow. Particularly we focus on the odd gravity moments, which reflect asymmetries between the northern and southern hemispheres and therefore are a pure signature of the dynamics with no contribution from the static planet. We use a hierarchy of models including a layered Concentric Maclaurin Spheroid model for determining the static component of the gravity spectrum, and an analysis of the vorticity balance for inferring the dynamical contribution to the gravity spectrum. In order to invert the gravity measurements into flow fields we use an adjoint based inverse model. Implications of the results regarding the dynamics governing the atmospheric and internal flows on Jupiter are discussed.