Storm-clouds brooding on towering heights

Abstract

Springtime on Saturn came in with a bang last December, when a massive storm erupted in its north temperate zone. This rare event has been observed in unprecedented detail from the ground and from space. See Letters p.71 & p.75 Six Great White Spot (GWS) events have been observed in the atmosphere of Saturn since 1876. These giant convective storms occur roughly once every Saturnian year (equal to 29.5 Earth years). The sixth GWS erupted in December 2010 and has been the subject of intense observation. Two papers in this issue present the details of some of these observations. Sanchez-Lavega et al. report that the storm developed at northern latitudes in the peak of a weak westward jet during early northern springtime. The storm head moved faster than the jet and triggered a disturbance that circled the planet. Numerical simulations show that Saturn's winds extend without decay deep down into the weather layer. Fischer et al. report that the storm reached a width of 10,000 kilometres within three weeks. Its lightning flash rates are an order of magnitude greater than those seen in previous storms, peaking at more than 10 flashes per second.