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Lightning storms on Saturn observed by Cassini ISS and RPWS during 2004-2006 |
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| Authors: | Ulyana A Dyudina Andrew P Ingersoll Carolyn C Porco William Kurth Anthony Del Genio Joseph Ferrier |
| Institution: | a 150-21, Geological and Planetary Sciences, Caltech, Pasadena, CA 91125, USA b CICLOPS, Space Science Institute, 4750 Walnut Street Suite 205, Boulder, CO 80301, USA c Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, IA 52242, USA d NASA-Goddard Space Flight Center, Code 695, Greenbelt, MD 20771, USA e NASA/Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA |
| Abstract: | We report on Cassini Imaging Science Subsystem (ISS) data correlated with Radio and Plasma Wave Science (RPWS) observations, which indicate lightning on Saturn. A rare bright cloud erupt at ∼35° South planetocentric latitude when radio emissions (Saturn Electrostatic Discharges, or SEDs) occur. The cloud consisting of few consecutive eruptions typically lasts for several weeks, and then both the cloud and the SEDs disappear. They may reappear again after several months or may stay inactive for a year. Possibly, all the clouds are produced by the same atmospheric disturbance which drifts West at 0.45 °/day. As of March 2007, four such correlated visible and radio storms have been observed since Cassini Saturn Orbit Insertion (July 2004). In all four cases the SEDs are periodic with roughly Saturn's rotation rate (h10m39), and show correlated phase relative to the times when the clouds are seen on the spacecraft-facing side of the planet, as had been shown for the 2004 storms in Porco, C.C., and 34 colleagues, 2005. Science 307, 1243-1247]. The 2000-km-scale storm clouds erupt to unusually high altitudes and then slowly fade at high altitudes and spread at low altitudes. The onset time of individual eruptions is less than a day during which time the SEDs reach their maximum rates. This suggests vigorous atmospheric updrafts accompanied by strong precipitation and lightning. Unlike lightning on Earth and Jupiter, where considerable lightning activity is known to exist, only one latitude on Saturn has produced lightning strong enough to be detected during the two and a half years of Cassini observations. This may partly be a detection issue. |
| Keywords: | Lightning Saturn atmosphere Atmospheres dynamics Meteorology Spectroscopy |
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