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Saturn’s rotation period from its atmospheric planetary-wave configuration

Abstract

The rotation period of a gas giant's magnetic field (called the System III reference frame) is commonly used to infer its bulk rotation1. Saturn's dipole magnetic field is not tilted relative to its rotation axis (unlike Jupiter, Uranus and Neptune), so the surrogate measure of its long-wavelength (kilometric) radiation is currently used to fix the System III rotation period2. The period as measured now by the Cassini spacecraft is up to 7 min longer3 than the value of 10 h 39 min 24 s measured 28 years ago by Voyager2. Here we report a determination of Saturn's rotation period based on an analysis of potential vorticity. The resulting reference frame (which we call System IIIw) rotates with a period of 10 h 34 min 13 ± 20 s. This shifted reference frame is consistent with a pattern of alternating jets on Saturn that is more symmetrical between eastward and westward flow. This suggests that Saturn's winds are much more like those of Jupiter than hitherto believed4.

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Figure 1: Variation of limiting planetary wave angular velocity with latitude for Saturn and Jupiter.
Figure 2: Comparison of cloud-level zonal velocity profiles on Saturn and Jupiter as viewed in System IIIw and System III.

References

  1. 1

    Seidelman, P. K. & Devine, N. Evaluation of Jupiter's longitudes in System III (1965). Geophys. Res. Lett. 4, 65–68 (1977)

    ADS  Article  Google Scholar 

  2. 2

    Desch, M. D. & Kaiser, M. L. Voyager measurement of the rotation period of Saturn’s magnetic field. Geophys. Res. Lett. 8, 253–256 (1981)

    ADS  Article  Google Scholar 

  3. 3

    Gurnett, D. A. et al. The variable rotation period of the inner region of Saturn's plasma disk. Science 316, 442–445 (2007)

    CAS  ADS  Article  Google Scholar 

  4. 4

    Aurnou, J. M. & Heimpel, M. H. Zonal jets in rotating convection with mixed mechanical boundary conditions. Icarus 169, 492–498 (2004)

    ADS  Article  Google Scholar 

  5. 5

    Giampieri, G., Dougherty, M. K., Smith, E. J. & Russell, C. T. A regular period for Saturn's magnetic field that may track its internal rotation. Nature 441, 62–64 (2006)

    CAS  ADS  Article  Google Scholar 

  6. 6

    Goldreich, P. & Farmer, A. J. Spontaneous axisymmetry breaking of the external magnetic field at Saturn. J. Geophys. Res. 112 A05225 10.1029/2006JA012163 (2007)

    CAS  ADS  Article  Google Scholar 

  7. 7

    Anderson, J. D. & Schubert, G. Saturn’s gravitational field, internal rotation, and interior structure. Science 317, 1384–1387 (2007)

    CAS  ADS  Article  Google Scholar 

  8. 8

    Dowling, T. E. A relationship between potential vorticity and zonal wind on Jupiter. J. Atmos. Sci. 50, 14–22 (1993)

    ADS  Article  Google Scholar 

  9. 9

    Dowling, T. E. Dynamics of Jovian atmospheres. Annu. Rev. Fluid Mech. 27, 293–334 (1995)

    ADS  MathSciNet  Article  Google Scholar 

  10. 10

    Dowling, T. E. Estimate of Jupiter’s deep zonal wind profile from Shoemaker-Levy 9 data and Arnol’d’s second stability criterion. Icarus 117, 439–442 (1995)

    ADS  Article  Google Scholar 

  11. 11

    Arnol’d, V. I. On an a priori estimate in the theory of hydrodynamical stability. [In Russian.] Izv. Vyssh. Ucheb. Zaved. Matematika 54, 3–5 (1966)

    Google Scholar 

  12. 12

    McIntyre, M. E. & Shepherd, T. G. An exact local conservation theorem for finite-amplitude disturbances to non-parallel shear flows with remarks on Hamiltonian structure and on Arnol’d stability theorems. J. Fluid Mech. 181, 527–565 (1987)

    ADS  MathSciNet  Article  Google Scholar 

  13. 13

    Charney, J. G. & Drazin, P. G. Propagation of planetary scale disturbances from the lower into the upper atmosphere. J. Geophys. Res. 66, 83–109 (1961)

    ADS  Article  Google Scholar 

  14. 14

    Lian, Y. & Showman, A. P. Deep jets on gas-giant planets. Icarus 194, 597–615 (2008)

    ADS  Article  Google Scholar 

  15. 15

    Ingersoll, A. P. & Pollard, D. Motion in the interiors and atmospheres of Jupiter and Saturn: scale analysis, anelastic equations, barotropic stability criterion. Icarus 52, 62–80 (1982)

    ADS  Article  Google Scholar 

  16. 16

    Read, P. L. et al. Mapping potential-vorticity dynamics on Jupiter. I: Zonal-mean circulation from Cassini and Voyager 1 data. Q. J. R. Meteorol. Soc. 132, 1577–1603 (2006)

    ADS  Article  Google Scholar 

  17. 17

    Read, P. L., Conrath, B. J., Fletcher, L. N., Gierasch, P. J. & Simon-Miller, A. A. Mapping potential vorticity dynamics on Saturn: zonal mean circulation from Cassini and Voyager data. Planet. Space. Sci. (in the press)

  18. 18

    Stone, P. H. Baroclinic adjustment. J. Atmos. Sci. 35, 561–571 (1978)

    ADS  Article  Google Scholar 

  19. 19

    Vasavada, A. R. & Showman, A. P. Jovian atmospheric dynamics: an update after Galileo and Cassini. Rev. Mod. Phys. 68, 1935–1996 (2005)

    MathSciNet  Google Scholar 

  20. 20

    Read, P. L. et al. Dynamics of convectively driven banded jets in the laboratory. J. Atmos. Sci. 64, 4031–4052 (2007)

    ADS  Article  Google Scholar 

  21. 21

    Stamp, A. P. & Dowling, T. E. Jupiter’s winds and Arnol’d’s second stability theorem: slowly moving waves and neutral stability. J. Geophys. Res. 98, 18847–18855 (1993)

    ADS  Article  Google Scholar 

  22. 22

    Helled, R., Schubert, G. & Anderson, J. D. Empirical models of pressure and density in Saturn's interior: implications for the helium concentration, its depth dependence, and Saturn's precession rate. Icarus 199, 368–377 (2009)

    ADS  Article  Google Scholar 

  23. 23

    Porco, C. C. et al. Cassini imaging of Jupiter’s atmosphere, satellites, and rings. Science 299, 1541–1547 (2003)

    CAS  ADS  Article  Google Scholar 

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Acknowledgements

We are grateful to F. M. Flasar and the Cassini CIRS team for access to the data from which the potential vorticity profiles discussed here were computed. P.L.R. acknowledges support from the UK Science and Technology Facilities Council, T.E.D. acknowledges support from NASA's Planetary Atmospheres and Outer Planet Research Programs, and G.S. acknowledges support from NASA’s Planetary Atmospheres and Planetary Geology and Geophysics programs. We are grateful also to R. Helled for computing values of ρ0 and J2 for Saturn based on System IIIw.

Author Contributions P.L.R. obtained and processed the Cassini data, deriving potential vorticity and ω(α) profiles, and conducted the statistical analysis. T.E.D. made the original suggestion to investigate α(φ) and contributed to the interpretation of the results. G.S. provided additional insights into Saturn’s rotation, and all authors contributed to the text and discussion of results.

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Read, P., Dowling, T. & Schubert, G. Saturn’s rotation period from its atmospheric planetary-wave configuration. Nature 460, 608–610 (2009). https://doi.org/10.1038/nature08194

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