Clouds and hazes vertical structure of a Saturn's giant vortex from Cassini/VIMS-V data analysis

We developed a forward radiative transfer model to describe Saturn's atmosphere and simulate VIMS-V spectra in the 0.35-1.05 μm wavelength range. The analysis has then been performed by means of an inverse model that we built on the basis of the Bayesian approach. Spatial distributions of effective radii, column number densities and top pressures of the cloud decks have been mapped and as a by-product of our analysis we also suggest a modified spectral shape for the imaginary part of the refractive index of the tropospheric haze, with respect to the shape described in the study of Karkoschka and Tomasko ([2005] Icarus, 179, 195-221).

The results suggest that the processes responsible for the formation and persistence of the vortex weakened between August 2011 and January 2012, even if the differences that we observe could be due to the fact that the vortex has moved in different positions between the two dates. We found that in August 2011 the upper haze was arranged in a dome like structure with the center at 8 mbar and the boundaries at 12 mbar; moreover we detected a zone in the lower haze at 135 mbar characterized by higher optical thickness with respect to the surrounding regions located at 85 mbar. In January 2012 the dome in the upper layer has diluted into a more homogeneous structure and the haze appears to be overall shifted to less than 6 mbar. Similarly, the 135 mbar high optical depth zone previously detected in the lower layer has disappeared.