Thermal Evolution of Saturn's 2010-2011 Disturbance

The remarkable disturbance that began in Saturn's northern hemisphere late in 2010 was initiated by a single discrete outburst of bright white cloud material, which spread with the prevailing zonal winds to completely encircle the planet within a matter of weeks. We report here the results of studies of the influence of the storm on thermal emission. These were obtained from thermal imaging observations between 5 and 25 μm, combining high-resolution imaging from ESO's Very Large Telescope (VLT) using the VISIR instrument and more frequent imaging from NASA's Infrared Telescope Facility (IRTF) using the MIRSI and NSFCam2 instruments. These observations were used to document the evolution of the spatial distributions of temperatures, gas composition and cloud opacity to trace the atmospheric circulation associated with the storm, which is consistent with a single convective plume in the deep clouds, sheared by the zonal winds and triggering widespread planetary wave activity. The disturbance generated the largest stratospheric thermal anomalies ever detected on Saturn (infrared 'beacons' that dominate the planetary emission), revealing dynamical coupling over hundreds of kilometers from the troposphere to the stratosphere. Observations made between January and March of 2011 revealed the presence of two stratospheric 'beacons' and only tropospheric cooling associated with the upwelling regions of the disturbance. Observations in April and thereafter showed that these 'beacons' had merged into a single feature, and that temperatures in the upper troposphere were increasing with time around the disturbance. Coincident with the disturbance, there appeared a major increase in the amplitude of zonal thermal waves in the northern hemisphere at longitudes distant from the disturbance. We note that the amplitude of zonal thermal waves in the southern hemisphere also increased. We will continue to track the evolution of this phenomenon, providing support for ground-based and Cassini spectroscopic observations.