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Since the Voyager 1 (V1) flyby in 1980, Titan's exploration from space and the ground has been ongoing for more than a full revolution of Saturn around the Sun (one Titanian year or 29.5 Earth years had elapsed in 2010 May). In this study, we search for temporal variations affecting Titan's atmospheric thermal and chemical structure within that year. We process Cassini/CIRS data taken during the Titan flybys from 2006-2013 and find a rather uneventful equatorial evolution. Conversely, at northern latitudes, we found enhanced abundances around the period of the northern spring equinox in mid-2009, which subsequently decreased (from 2010 to 2012), returning to values similar to those found in the V1 epoch, one Titanian year before. In the southern latitudes, since 2012, we see a trend for an increase of several trace gases (C4H2, C3H4, and HCN), indicative of a seasonal atmospheric reversal setting in. When we compare the CIRS 2010 and the 1980 V1/IRIS spectra (reanalyzed here), we find limited inter-annual variations. A return to the 1980 stratospheric temperatures and abundances is generally achieved from 50°N to 50°S, indicative of the solar radiation being the dominating energy source at 10 AU, as for the Earth, as predicted by general circulation and photochemical models. Exceptions concern the most complex hydrocarbons (C4H2 and C3H4). We also consider data from ground-based and Earth-orbiting observatories (such as from the Infrared Space Observatory, revisited here) and discuss possible atmospheric composition trends during a Titanian year. [ABSTRACT FROM AUTHOR]

Stratospheric temperatures on Saturn imply a strong decay of theequatorial winds with altitude. If the decrease in winds reported fromrecent Hubble Space Telescope images is not a temporal change, then thefeatures tracked must have been at least 130 kilometers higher than inearlier studies. Saturn's south polar stratosphere is warmer thanpredicted from simple radiative models. The C/H ratio on Saturn is seventimes solar, twice Jupiter's. Saturn's ring temperatures have radialvariations down to the smallest scale resolved (100 kilometers). Diurnalsurface temperature variations on Phoebe suggest a more porous regoliththan on the Jovian satellites. [ABSTRACT FROM AUTHOR]

We have developed a line-by-line Atmospheric Radiative Transfer for Titan code that includes the most recent laboratory spectroscopic data and haze descriptions relative to Titan's stratosphere. We use this code to model Cassini Composite Infrared Spectrometer data taken during the numerous Titan flybys from 2006 to 2012 at surface-intercepting geometry in the 600-1500 cm–1 range for latitudes from 50°S to 50°N. We report variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE). We find indication for a weakening of the temperature gradient with warming of the stratosphere and cooling of the lower mesosphere. In addition, we infer precise concentrations for the trace gases and their main isotopologues and find that the chemical composition in Titan's stratosphere varies significantly with latitude during the 6 years investigated here, with increased mixing ratios toward the northern latitudes. In particular, we monitor and quantify the amplitude of a maximum enhancement of several gases observed at northern latitudes up to 50°N around mid-2009, at the time of the NSE. We find that this rise is followed by a rapid decrease in chemical inventory in 2010 probably due to a weakening north polar vortex with reduced lateral mixing across the vortex boundary. [ABSTRACT FROM AUTHOR]