Saturn's Seasonal Winds and Temperature: the Effect of the Ring System on the Troposphere and Stratosphere

The radiative properties of Saturn's rings (insolation shadowing, insolation scattering, and thermal emission) have been incorporated into a seasonal, zonally-averaged, radiative-dynamical model to investigate the magnitude of small seasonal fluctuations in the troposphere and stratosphere of Saturn. Although the radiative time constant is large in Saturn's troposphere and stratosphere, the rings induce significant latitudinal insolation gradients resulting in potential disturbances in the upper stratosphere. The results of the model are compared to the Pioneer and Voyager Radio Sub-System (RSS) vertical temperature profile measurements and to the Voyager Infrared Interferometric Spectrometer (IRIS) latitudinal temperature profile measurements. In the upper stratosphere (1 to 30 mBar) the heating is dominated by methane and the model can be directly compared to the Voyager data. Below the temperature minimum ( ~100 mBar) the radiative time constant is sufficiently long to strongly dampen seasonal variations, however, the temperature excursions seen in the IRIS data are significantly larger than those predicted by the radiative model. The thermal effects of the strong Saturnian zonal winds are simulated with a first-order dynamical model to provide some insight into the lower boundary conditions. The remaining differences between the model and the Voyager IRIS data-sets are used to estimate the quantity of aerosol (a free parameter in this model) required near the tropopause region. The magnitudes of the wind and temperature perturbations, caused by the radiative effects of Saturn's rings, are discussed in the context of the future Hubble Space Telescope and the planned Cassini Saturnian Orbiter missions.