Seasonal Evolution of Saturn's Polar Atmosphere from a Decade of Cassini/CIRS Observations
Abstract
Saturn's polar regions are subjected to extreme insolation variations over its 29.5 year orbit due to the gas giant's 26-degree axial tilt, causing seasonal changes to the thermal structure, chemistry, dynamics and cloud properties of the polar environments. Cassini's high inclination orbits permit detailed scrutiny of Saturn's high latitudes in a dataset that now spans a decade (a third of a Saturn year, 2004-2014), five years either side of the northern spring equinox in 2009. Thermal infrared Cassini/CIRS spectra (7-16 μm) from all mission phases are inverted to determine the rate of change of polar temperatures, wind shears, tropospheric phosphine (as a tracer of vertical mixing) and stratospheric hydrocarbons (tracers of middle atmospheric circulation and chemistry). Cassini's unique vantage point allows us to track these parameters as the summer southern pole receded into autumn and the winter northern pole emerged into spring sunlight. Results show the most rapid changes to temperature and composition occurring poleward of 70o in each hemisphere, in excess of expectations from simple radiative climate models. Small cyclonic vortices persist at both poles throughout theCassini mission, while the broad stratospheric vortices are seasonally variable. The signature of the northern hexagon is still present in the tropospheric thermal structure. At the time of writing, an infraredbright polar vortex is beginning to emerge at the northern spring pole, consistent with the historical record of Saturn observations from the 1980s (previous northern spring, [4]).
- Publication:
-
European Planetary Science Congress
- Pub Date:
- April 2014
- Bibcode:
- 2014EPSC....9...62F