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S. Pérez-Hoyos, A. Sánchez-Lavega, J.F. Rojas (Universidad del País Vasco), R.G. French (Wellesley College)
In this work we present a photometric study of Saturn's Southern Hemisphere based on the Hubble Space telescope yearly campaigns from 1996 to 2002. More than a hundred images, mainly taken with the WFPC2 in a wide spectral coverage from 218nm to 1042nm, were calibrated in order to obtain the absolute reflectivity variations from limb to limb at selected latitudes. Using a radiative transfer code based on the ``doubling-adding" technique, we modelled the observed data in order to constrain the vertical location and density of clouds and aerosols in the upper atmosphere (from 1 mbar to ~ 2bar) and the optical properties of the particles they are formed of. We have studied latitudes from equator to pole with a standard model that includes scattering and gas (methane) absorption and three layers of particles forming a thin stratospheric haze, a tropospheric haze close to the tropopause level and a semi-infinite tropospheric cloud, putatively formed by ammonia ice. We have detected only slight variations in the particle properties and in the height of the hazes, but a noticeably variation in the optical depth of the tropospheric haze from 1996 to 2002, identifying some short-termed features probably associated with dynamical phenomena. The final goal of this project is to constrain a mean model of the cloud structure for the whole Southern Hemisphere before the arrival of the Cassini mission in 2004, studying its variation from year to year, and trying to separate the possible long-term seasonal and ring-shadowing effects, from other dynamical changes. Acknowledgements: This work was supported by the Spanish MCYT PNAYA 2000-0932. SPH acknowledges a PhD fellowship from the Spanish MECD. RGF was supported in part by NASA's Planetary Geology and Geophysics Program NAG5-10197 and STSCI Grant GO-08660.01A.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.