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J.L. Ollivier, M. Dobrijevic, J.P. Parisot (Observatoire de Bordeaux)
The results of a new photochemical model of Saturn's atmosphere are presented. This model derives from the model of Neptune developed by Dobrijévic et al. (1998). This 1-D photochemical code includes hydrocarbons and oxygen compounds. Vertical transport is driven by molecular and eddy diffusion. External fluxes are also included. Photodissociation rates are determined using a radiative transfer treatment which takes multiple scattering into account. We compare the results to Voyager data, groundbased observations, and recent ISO data. Reproducing methane mole fraction observations gives constraints on its tropospheric mole fraction and eddy diffusion profile. Using these parameters leads to an overabundance of methyl radical in comparison with ISO results (Bézard et al. 1998) and to an underestimation of the abundance of higher hydrocarbons. Possible explanations are: (i) higher recombination rates of CH3, (ii) chemical process not included in the model. External fluxes of oxygenated materials have been included. We find a good agreement with ISO observations (Feuchtgruber et al. 1997): \sigmaH_2O=6.8~1014 molecules~cm-2 and \sigmaCO_2=7.3~1014 molecules~cm-2 with external fluxes \PhiH_2O=106 molecules~cm-2s-1, \PhiCO=2~105 molecules~cm-2 s-1 and \PhiCO_2=6~104 molecules~cm-2s-1. Relative proportion of these fluxes is equal to the mean composition of comets (CO/H2O=0.2, CO2/H2O=0.06 from Despois, 1998). CO has also an internal origin, as these external fluxes can't reproduce the abundance of CO derived by Noll & Larson (1990).
The author(s) of this abstract have provided an email address for comments about the abstract: ollivier@planet.observ.u-bordeaux.fr