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Disruption of Saturn’s quasi-periodic equatorial oscillation by the great northern storm


The equatorial middle atmospheres of the Earth1, Jupiter2 and Saturn3,4 all exhibit a remarkably similar phenomenon—a vertical, cyclic pattern of alternating temperatures and zonal (east–west) wind regimes that propagate slowly downwards with a well-defined multi-year period. Earth’s quasi-biennial oscillation (QBO) (observed in the lower stratospheric winds with an average period of 28 months) is one of the most regular, repeatable cycles exhibited by our climate system1,5,6, and yet recent work has shown that this regularity can be disrupted by events occurring far away from the equatorial region, an example of a phenomenon known as atmospheric teleconnection7,8. Here, we reveal that Saturn’s equatorial quasi-periodic oscillation (QPO) (with an ~15-year period3,9) can also be dramatically perturbed. An intense springtime storm erupted at Saturn’s northern mid-latitudes in December 201010,11,12, spawning a gigantic hot vortex in the stratosphere at 40° N that persisted for three years13. Far from the storm, the Cassini temperature measurements showed a dramatic ~10 K cooling in the 0.5–5 mbar range across the entire equatorial region, disrupting the regular QPO pattern and significantly altering the middle-atmospheric wind structure, suggesting an injection of westward momentum into the equatorial wind system from waves generated by the northern storm. Hence, as on Earth, meteorological activity at mid-latitudes can have a profound effect on the regular atmospheric cycles in Saturn’s tropics, demonstrating that waves can provide horizontal teleconnections between the phenomena shaping the middle atmospheres of giant planets.

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Fig. 1: Saturn’s stratospheric temperatures at 1 mbar determined by Cassini/CIRS.
Fig. 2: Snapshots of Saturn’s equatorial temperatures and winds during the 13-yr time series in Fig. 1.
Fig. 3: Hovmöller diagrams showing the downward propagation of the QPO thermal and wind patterns and the 2011–2014 disruption.


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L.N.F. was supported by a Royal Society Research Fellowship and European Research Council Consolidator Grant (under the European Union’s Horizon 2020 research and innovation programme, grant agreement no. 723890) at the University of Leicester. The UK authors acknowledge the support of the Science and Technology Facilities Council. S.G. and T.F. were supported by the Centre national d'études spatiales. A portion of this work was completed by G.S.O. at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We are extremely grateful to all those Cassini team members involved in the planning, execution and reduction of the CIRS data, without whom this study would not have been possible. This investigation was partially based on VLT observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere (see Extended Data for ESO program IDs); and on data acquired by the Subaru Telescope operated by the National Astronomical Observatory of Japan, and extracted from the SMOKA database (program IDs are provided in the Extended Data).

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L.N.F. was responsible for analysing the nadir data and writing the article. S.G. and T.F. analysed Cassini limb observations and assisted with the nadir–limb comparison and calculation of zonal winds. L.L. provided a cross-comparison of zonal winds via a different algorithm, and F.M.F. provided assistance with the wind calculations. G.S.O. assisted with the ground-based observing campaign. P.G.J.I. developed the software to permit inversions of Cassini/CIRS spectra. N.G. generated the CIRS spectral database. All authors read and commented on the manuscript.

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Correspondence to Leigh N. Fletcher.

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Fletcher, L.N., Guerlet, S., Orton, G.S. et al. Disruption of Saturn’s quasi-periodic equatorial oscillation by the great northern storm. Nat Astron 1, 765–770 (2017).

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