Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.0403m&link_type=abstract
American Astronomical Society, DPS meeting #39, #4.03; Bulletin of the American Astronomical Society, Vol. 39, p.413
Astronomy and Astrophysics
Astronomy
Scientific paper
Cassini and ground-based thermal-infrared observations have revealed several puzzles regarding composition and temperatures in Saturn's stratosphere. One of the most interesting puzzles is the different latitudinal distribution of ethane and acetylene. The ethane mixing ratio near the 2 mbar level is observed to be constant or even to increase with latitude in the southern (summer) hemisphere, whereas the acetylene mixing ratio near 1 mbar decreases with latitude (e.g., Greathouse et al. 2005, Howett et al. 2007). One-dimensional photochemical models can explain the meridional distribution of C2H2 but not C2H6 (Moses and Greathouse 2005). The distribution of photochemically long-lived ethane is clearly being affected by horizontal transport, whereas shorter-lived acetylene more closely tracks the solar insolation. We therefore have developed a two-dimensional photochemistry/transport model to investigate the distribution of trace atmospheric constituents as a function of latitude, altitude, and time in Saturn's stratosphere. The model includes advection and diffusion (vertical and meridional), hydrocarbon and oxygen photochemistry, aerosol condensation and evaporation, and radiative transfer. Variations in ultraviolet flux due to orbital position, season, and ring shadowing are considered. As with the 2-D Jupiter modeling of Liang et al. (2005), we find that the chemistry of C2H2 and C2H6 is intricately linked, especially in the middle stratosphere, where ethane photolysis is a major contributor to acetylene production. Because of this chemical coupling between C2H2 and C2H6, circulation and horizontal diffusion scenarios that redistribute C2H6 with latitude tend to result in a C2H2 distribution that mimics the C2H6 distribution. We will present the results from our 2-D photochemistry/transport models and discuss how the current model-data mismatch might be resolved.
Liang Mao-Chang
Moses Julianne I.
Shia Run-Lie
Yung Yuk L.
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