Abstract for fall AGU, San Francisco (3-7 December 2012) 

Planned for Session AE002 (Electrification Processes, Lightning and other Discharge Phenomena in Planetary Surfaces and Atmospheres) 

Thunderstorm and lightning observations during 
and after the Great White Spot event on Saturn



G. Fischer (1), K. Sayanagi (2), D.A. Gurnett (3), W.S. Kurth (3), 
U.A. Dyudina (4), A.P. Ingersoll (4), M. Delcroix (5), A. Wesley (6), and T. Barry (7)



(1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria

(2) Dept. of Atmospheric and Planetary Sciences, Hampton Univ., Hampton, USA

(3) Dept. of Physics and Astronomy, Univ. of Iowa, Iowa City, USA

(4) Division of Geological and Planetary Sciences, Caltech, Pasadena, USA

(5) Societe Astronomique de France, Tournefeuilee, France

(6) Murrumbateman, Australia
(7) Astronomical Society of New South Wales, Australia



The giant thunderstorm called Great White Spot (GWS) emitted radio waves associated 
with Saturn lightning discharges from 5 December 2010 until 28 August 2011. We will 
present the most important physical characteristics of this powerful lightning storm. 
Flash rates were extremely high (~10 per second) from mid-December until 20 June. On 
that day a feature that was identified as an anticyclonic vortex in the Cassini images 
met the so-called head of the storm, where most lightning flashes originated from. 
After the head-vortex collision the lightning rates first steeply declined, then waxed 
and waned until the signals became undetectable in early August. The radio signals resurged in late August for 9 days on a weak level, and the source clouds could be 
identified in the Cassini images.

The lightning activity after the GWS event showed a few weak episodes around September/
October and late December 2011, which probably originated from minor thunderstorm cells 
located in the former tail of the GWS at 35 deg. north kronocentric latitude. A more 
stable lighting storm of 2000 km in size developed at the end of March and lasted until 
21 April 2012. Ground-based images showed an associated white spot at a latitude of 
50 deg. north. This is the first time that a thunderstorm has been identified at this 
latitude, which, similar to other storms, is coinciding with a minimum in zonal wind 
speed in Saturn's atmosphere. It is possible that the spot at 50 deg. north was already 
a moderatly active lightning source in January 2011 during the intense GWS event, and that it showed another small outbreak in July 2012.