36th DPS Meeting, 8-12 November 2004
Session 18 Outer Planets
Poster I, Tuesday, November 9, 2004, 4:00-7:00pm, Exhibition Hall 1A

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[18.14] Seasonal/Latitudinal Models of Stratospheric Photochemistry on Saturn

J. I. Moses, T. K. Greathouse (LPI)

To date, most investigations of stratospheric photochemistry on the outer planets have involved one-dimensional (1-D) ``global-average'' or single-latitude models for a single season. With Cassini CIRS poised to map hydrocarbon distributions across Saturn, and with advances in detector technology and telescope size for Earth-based observations allowing composition and temperatures to be derived as a function of latitude, we are now in a position to evaluate the effectiveness of 1-D models in describing the stratospheric composition. Are 2-D models that include meridional transport necessary to reproduce the observed hydrocarbon latitudinal distributions, or can 1-D seasonal models provide an accurate description? In order to evaluate these questions, we have developed a realistic, time-variable, 1-D seasonal model for stratospheric photochemistry on Saturn. The model accounts for variations in orbital position and in ultraviolet flux due to solar-cycle variations and ring-shadow effects. The results for one Saturnian year, starting at Ls = 0\circ in 1980 and running until the next vernal equinox in 2009, are presented for numerous latitudes. Due to the long vertical diffusion time scale at pressures greater than ~1 mbar, we find that seasonal effects are more pronounced at high altitudes. In addition, a phase lag between insolation and chemical response increases with increasing pressure. In the summer hemisphere, hydrocarbon abundances do not exhibit much variation with latitude because the increase in the length of the day with increasing latitude counterbalances the increasing solar zenith angle, causing the daily-averaged insolation to remain nearly constant over a wide range of latitudes. Latitudinal variations are more pronounced during other seasons. We compare our model results with various observations.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.