The structure of Jupiter and Saturn's winds below the cloud level - insights from high harmonics gravity measurements

Strong and persistent zonal winds at the cloud level characterize both Jupiter and Saturn. Based on  Juno and Cassini's measurements of the low-order gravity harmonics up to J₁₀,  it was shown that the observed cloud-level winds penetrate inward parallel to the planet's spin axis and decay at a depth of around 3,000 km and 9,000 km, respectively. However, because of the limited number of measured gravity harmonics, the latitudinal structure of the flows could not be uniquely determined, so only an overall estimate of their depth was obtained.

Here, we present new gravity analyses for both gas giants, based on the original Juno and Cassini measurements,  but in which the magnitude of harmonics higher than J₁₀ is constrained at the less observable high latitudes. This enables resolving the gravity field up to J₄₀ for Jupiter and J₂₀ for Saturn, while being consistent with the previous gravity measurements.  We then use the high harmonics to better constrain the structure of the zonal flows below the observed cloud level, revealing the latitudinal variations in the depth of the flows. We show that for Saturn, the mid-to-high latitude jets must be shallower than the low-latitude winds, while in Jupiter, the low-latitude winds dominate the gravity signal. In the talk, we will review the similarities and differences between the two gas giants arising from our results and discuss their implications for our understanding of gas giant dynamics.