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Equatorial winds on Saturn and the stratospheric oscillation

Nature Geoscience volume 4, pages 750–752 (2011)Cite this article

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Abstract

The zonal jets on the giant planets have been thought to be stable in time1,2,3. A decline in the velocity of Saturn’s equatorial jet has been identified, on the basis of a comparison of cloud-tracking data across two decades4, but the differences in cloud speeds have since been suggested to stem from changes in cloud altitude in combination with vertical wind shear, rather than from temporal changes in wind strength at a given height5. Here, we combine observations of cloud tracks and of atmospheric temperatures taken by two instruments on the Cassini spacecraft to reveal a significant temporal variation in the strength of the high-altitude equatorial jet on Saturn. Specifically, we find that wind speeds at atmospheric pressure levels of 60 mbar, corresponding to Saturn’s tropopause, increased by about 20 m s−1 between 2004 and 2008, whereas the wind speed has been essentially constant over time in the southern equatorial troposphere. The observations further reveal that the equatorial jet intensified by about 60 m s−1 between 2005 and 2008 in the stratosphere, that is, at pressure levels of 1–5 mbar. Because the wind acceleration is weaker near the tropopause than higher up, in the stratosphere, we conclude that the semi-annual equatorial oscillation of Saturn’s middle atmosphere6,7 is also damped as it propagates downwards.

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Figure 1: Southern equatorial maps based on ISS multifilter images taken on 10 May 2004.
Figure 2: Saturn wind measurements on different dates.

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Acknowledgements

NASA Cassini Data Analysis Program funded this work. We acknowledge E. Garcia-Melendo, R. Hueso, A. Sanchez-Lavega, and S. Perez-Hoyos for providing comments and discussions. We are also grateful for comments and suggestions on this work from two anonymous reviewers.

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Authors and Affiliations

  1. Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204, USA

    Liming Li & Xun Jiang

  2. Division of Geological and Planetary Sciences, Caltech, Pasadena, California 91125, USA

    Andrew P. Ingersoll & Shawn P. Ewald

  3. NASA Goddard Institute for Space Studies, New York, New York 10025, USA

    Anthony D. Del Genio

  4. CICLOPS/Space Science Institute, Boulder, Colorado 80301, USA

    Carolyn C. Porco

  5. Jet Propulsion Laboratory, Caltech, Pasadena, California 91109, USA

    Robert A. West, Ashwin R. Vasavada, Glenn S. Orton & Kevin H. Baines

  6. Department of Astronomy, Cornell University, Ithaca, New York 14853, USA

    Barney J. Conrath & Peter J. Gierasch

  7. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    Amy A. Simon-Miller

  8. Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA

    Conor A. Nixon & Richard K. Achterberg

  9. Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford OX1 3PU, UK

    Leigh N. Fletcher

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  1. Liming Li
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  16. Kevin H. Baines
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Contributions

L.L. measured the ISS winds (correlated), computed the thermal winds and conceived the overall research. X.J. carried out the ISS wind measurements (cloud tracking). X.J., A.P.I., A.D.D.G., C.C.P., R.A.W., A.R.V., S.P.E., B.J.C., P.J.G., A.A.S-M., C.A.N., R.K.A., G.S.O., L.N.F. and K.H.B. provided assistance in interpreting the observational results.

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Correspondence to Liming Li.

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The authors declare no competing financial interests.

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Li, L., Jiang, X., Ingersoll, A. et al. Equatorial winds on Saturn and the stratospheric oscillation. Nature Geosci 4, 750–752 (2011). https://doi.org/10.1038/ngeo1292

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