A large cloud outburst at Titanʹs south pole

Images of Titan acquired over five nights in October 2004 using the adaptive optics system at the Keck Observatory show dramatic increases in tropospheric cloud activity at the south pole compared with all other images of Titan clouds to date. During this time, Titanʹs south polar clouds brightened to more than 18 times their typical values. The Cassini Ta flyby of Titan occurred as this storm was rapidly dissipating. We find that the brightness of this cloud outburst is consistent with the dramatic transient brightening of Titan observed in atmospheric windows on two nights in 1995 by Griffith et al. [Griffith, C.A., Owen, T., Miller, G.A., Geballe, T., 1998. Nature 395 (6702) 575–578] if we scale the brightness of the cloud by projecting it onto the equator. While apparently infrequent, the fact that large cloud events have been observed in different seasons of Titanʹs year indicates that these large storms might be a year-round phenomenon on Titan. We propose possible mechanisms to explain these occasional short-term increases in Titanʹs cloud activity.