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Impacts of zonal winds on planetary oscillations and Saturn ring seismology

Dewberry, Janosz W. and Mankovich, Christopher R. and Fuller, Jim (2022) Impacts of zonal winds on planetary oscillations and Saturn ring seismology. Monthly Notices of the Royal Astronomical Society, 516 (1). pp. 358-371. ISSN 0035-8711. doi:10.1093/mnras/stac1957.

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The excitation of density and bending waves in Saturn’s C ring by planetary oscillation modes presents a unique opportunity to learn about gas giant interiors and rotation. However, theoretical complications related to Saturn’s rapid and differential rotation pose a barrier to the full utilization of ring wave detections. We calculate oscillation modes using a complete, non-perturbative treatment of differential rotation modelled after Saturn’s zonal winds in self-consistently computed, polytropic equilibria. We find that previous, approximate treatments of the effects of differential rotation in Saturn overestimate shifts in the frequencies of fundamental modes (f modes) thought to be responsible for the majority of the waves detected in the C ring, due to an omitted modification of the equilibrium shape and structure of the planet by differential rotation. The bias introduced by these frequency overestimates is small, but significant relative to the uncertainties afforded by Cassini data. We additionally consider the non-perturbative effects of Saturn-like differential rotation on the rotational mixing of f modes and internal gravity modes (g modes), which is relevant to detections of multiple density waves with very closely split pattern speeds. We find that higher-order rotational effects can produce orders-of-magnitude enhancements in the surface gravitational perturbations of g modes dominated by large spherical harmonic degrees ℓ, regardless of frequency separation from the sectoral f mode. Despite this enhancement, we find that the observed fine splitting of density waves is unlikely to involve g modes dominated by ℓ ≳ 10. This restriction may aid in the inference of possible internal structures for Saturn.

Item Type:Article
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URLURL TypeDescription article
Dewberry, Janosz W.0000-0001-9420-5194
Mankovich, Christopher R.0000-0002-4940-9929
Fuller, Jim0000-0002-4544-0750
Additional Information:We thank Mark S. Marley for reviewing this work and for providing helpful comments that improved the quality of the paper. We are thankful for support from the Caltech Center for Comparative Planetary Evolution. JWD gratefully acknowledges support from the Sloan Foundation through grant FG-2018-10515, and from the Natural Sciences and Engineering Research Council of Canada (NSERC) [funding reference #CITA 490888-16].
Group:Astronomy Department
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada#CITA 490888-16
Sloan FoundationFG-2018-10515
Issue or Number:1
Record Number:CaltechAUTHORS:20220906-252590000
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116721
Deposited By: Olivia Warschaw
Deposited On:07 Sep 2022 22:48
Last Modified:07 Sep 2022 22:48

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