Cassini Radio Occultations of Saturn's Ionosphere: Modeling a Variable Influx of Water into Saturn's Atmosphere

Details Cassini Radio Occultations of Saturn's Ionosphere: Modeling a Variable Influx of Water into Saturn's Atmosphere Cassini Radio Occultations of Saturn's Ionosphere: Modeling a Variable Influx of Water into Saturn's Atmosphere

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p41c1293m&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P41C-1293

Physics

5729 Ionospheres (2459), 6275 Saturn, 6929 Ionospheric Physics (1240, 2400), 6934 Ionospheric Propagation (0689, 2487, 3285, 4275, 4455)

Scientific paper

The Saturn-Thermosphere-Ionosphere-Model (STIM), a global circulation model (GCM) of Saturn's upper atmosphere, is used to investigate a range of possible parameters that could lead to the profiles measured recently by the Radio Science Subsystem (RSS) aboard Cassini. Specifically, electron density observations of Saturn's equatorial ionosphere demonstrate a dawn/dusk asymmetry, a possible double peak, and a high degree of vertical structure and variability. On average, peak electron densities are larger at dusk than dawn (5400 cm-3 vs. 1700 cm-3) and the peak altitudes are lower at dusk than dawn (1880 km vs. 2360 km). Self-consistent, time-dependent 1D water diffusion calculations have been combined with the GCM in order to examine the possibility that a topside flux of neutral water into Saturn's atmosphere may provide a loss mechanism -- via charge exchange with protons -- that is sufficient to reproduce the observed ionosphere. Our previous modeling results indicated that a constant background influx of (0.5 -- 1.0) x 107 H2O cm-2 sec-1 was adequate in reproducing Cassini measurements on average [Moore et al., 2006], however the large observed variations in the vertical electron density profiles require additional complexities in the modeling. In this study we show that one possible source of the structuring observed in the electron density profiles could be from brief surges and/or reductions in the background water flux, which ultimately may be linked to geysers near Enceladus' southern pole. Moore, L., A.F. Nagy, A.J. Kliore, I. Mueller-Wodarg, J.D. Richardson, M. Mendillo (2006), Cassini radio occultations of Saturn's ionopshere: I. model comparisons using a constant water flux, submitted to GRL.

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