Observational constraints on the strength and depth of the zonal jets on Saturn

Saturn is characterized by strong zonal winds at the cloud level, with a wide equatorial west-to-east flow, two retrograde jets on its flanks, and a series of mid-to-high latitude jets in both hemispheres. Based on the Cassini mission gravity measurement up to zonal harmonic J10, it was shown that these winds penetrate to approximately 9000 km. However, these analyses relied fully on the low, even harmonics dominated by an interior structure that is not known to high accuracy. Here, we present a Cassini-based gravity analysis, resolving the gravity harmonics up to J20, by constraining the surface gravity in the polar regions. Using the extended harmonics and surface gravity, we show evidence that the wind structure poleward of latitude 45° must be shallower than 3000 km, while equatorward, the wind must extend along cylinders and decayed radially at a depth of approximately 11,000 km. We also find that nearly doubling the wind strength, while keeping its latitudinal structure, allows for an excellent fit to all 20 measured gravity harmonics, suggesting that the zonal jets reach their maximum strength below the observed cloud level.