Li, Liming and Jiang, Xun and Ingersoll, Andrew P. and Del Genio, Anthony D. and Porco, Carolyn C. and West, Robert A. and Vasavada, Ashwin R. and Ewald, Shawn P. and Conrath, Barney J. and Gierasch, Peter J. and Simon-Miller, Amy A. and Nixon, Conor A. and Achterberg, Richard K. and Orton, Glenn S. and Fletcher, Leigh N. and Baines, Kevin H. (2011) Equatorial winds on Saturn and the stratospheric oscillation. Nature Geoscience, 4 (11). pp. 750-752. ISSN 1752-0894 http://resolver.caltech.edu/CaltechAUTHORS:20111207-143142776
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The zonal jets on the giant planets have been thought to be stable in time. 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 decades, 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 height. 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 atmosphere is also damped as it propagates downwards.
|Additional Information:||© 2011 Macmillan Publishers Limited. Received 16 February 2011. Accepted 14 September 2011. Published online 16 October 2011. 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. Author 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.|
|Official Citation:||Equatorial winds on Saturn and the stratospheric oscillation - pp750 - 752 Liming Li, Xun Jiang, Andrew P. Ingersoll, Anthony D. Del Genio, Carolyn C. Porco, Robert A. West, Ashwin R. Vasavada, Shawn P. Ewald, Barney J. Conrath, Peter J. Gierasch, Amy A. Simon-Miller, Conor A. Nixon, Richard K. Achterberg, Glenn S. Orton, Leigh N. Fletcher & Kevin H. Baines doi:10.1038/ngeo1292|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||07 Dec 2011 22:53|
|Last Modified:||07 Dec 2011 22:53|
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