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A giant thunderstorm on Saturn

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Abstract

Lightning discharges in Saturn’s atmosphere emit radio waves1 with intensities about 10,000 times stronger than those of their terrestrial counterparts2. These radio waves are the characteristic features of lightning from thunderstorms on Saturn, which last for days to months2. Convective storms about 2,000 kilometres in size have been observed in recent years at planetocentric latitude 35° south3,4,5 (corresponding to a planetographic latitude of 41° south). Here we report observations of a giant thunderstorm at planetocentric latitude 35° north that reached a latitudinal extension of 10,000 kilometres—comparable in size to a ‘Great White Spot’6,7—about three weeks after it started in early December 2010. The visible plume consists of high-altitude clouds that overshoot the outermost ammonia cloud layer owing to strong vertical convection, as is typical for thunderstorms. The flash rates of this storm are about an order of magnitude higher than previous ones, and peak rates larger than ten per second were recorded. This main storm developed an elongated eastward tail with additional but weaker storm cells that wrapped around the whole planet by February 2011. Unlike storms on Earth, the total power of this storm is comparable to Saturn’s total emitted power. The appearance of such storms in the northern hemisphere could be related to the change of seasons7, given that Saturn experienced vernal equinox in August 2009.

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Figure 1: Time-frequency spectrogram of the SED episode on 12 December 2010.
Figure 2: Saturn’s lightning activity and Cassini’s distance to Saturn as a function of time for December 2010.
Figure 3: Images of Saturn with the storm.
Figure 4: False-colour views showing the height of the storm clouds.

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Acknowledgements

G.F. was supported by the Austrian Science Fund (FWF). Cassini research at the University of Iowa was funded by NASA/JPL. We thank A. Sánchez-Lavega for launching an alert on the webpage of the Planetary Virtual Observatory and Laboratory (http://www.pvol.ehu.es), and the amateur astronomers who subsequently observed the storm on Saturn, namely, T. Akutsu, T. Barry, J. Castella, D. Chang, D. Gray, J. B. Jovani, W. Kivits, T. Kumamori, F. J. Melillo, D. Parker, D. Peach, J. Phillips, J.-J. Poupeau, J. Sussenbach, K. Yunoki and S. Walker. S. Ghomizadeh and T. Ikemura were the first to observe the storm before the alert.

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Contributions

G.F. analysed Cassini RPWS data and wrote the paper. W.S.K., D.A.G. and P.Z. helped in this analysis. U.A.D., A.P.I., S.P.E. and C.C.P. analysed the Cassini ISS image and calculated the energy of the storm. A.W. and C.G. imaged Saturn from the ground, and M.D. measured the size and drift of the storm from several images. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to G. Fischer.

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The authors declare no competing financial interests.

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Fischer, G., Kurth, W., Gurnett, D. et al. A giant thunderstorm on Saturn. Nature 475, 75–77 (2011). https://doi.org/10.1038/nature10205

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