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Exploring Saturn’s wind depth using high gravity harmonics

Presentation #302.02 in the session Giant Planet Interior Structure and Dynamics (Oral Presentation)

Published onOct 23, 2023
Exploring Saturn’s wind depth using high gravity harmonics

Saturn is characterized by strong zonal winds at the cloud level, with a ~300 m/s wide equatorial west-to-east flow, two ~100 m/s retrograde jets on its flanks, and a series of ~100 m/s mid-to-high latitude jets in both hemispheres. Based on the Cassini measurements of gravity harmonics up to J10, and using thermal wind balance, it was shown that these winds penetrate inward parallel to the planet’s spin axis and decay at a depth of around 9,000 km. However, the analysis relied on the low-even harmonics provided by interior structure models, as the measured low-odd harmonics (purely wind-induced) were primarily close to the measurement uncertainty. In addition, in all previous studies, the zonal wind penetrating into the deep atmosphere had to be somewhat different from the observed cloud-level wind to match the gravity data.

Here we present a new Cassini-based gravity analysis in which the magnitude of harmonics higher than J10 are constrained at the less observable high latitudes. This enables resolving the gravity field up to J20 while consistent with the previous gravity measurements. We then use the high harmonics to constrain better the structure of the zonal flows below the observed cloud level. We show that under certain assumptions, it is possible to explain all the measured wind-induced gravity harmonics using the observed winds. We also discuss the implications of our results for Saturn’s atmospheric dynamics and interior structure.

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