Cassini radio occultations of Saturn’s ionosphere: Model comparisons using a constant water flux

[1] Recent radio occultations of Saturn’s equatorial ionosphere by the Cassini spacecraft provide important insight into this poorly constrained region. Twelve new electron density profiles identify a clear dawn/dusk asymmetry as well as two apparently separate electron density peaks. This study uses a 3D general circulation model along with 1D water diffusion calculations 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 ionosphere observed by Cassini. Results indicate that a constant influx of water of (0.5–1.0) 10 H2O cm 2 sec 1 is adequate for reproducing Cassini measurements, providing a good match to the main electron density peak at dawn and dusk. In addition, these calculations use a reduced rate for the reaction H + H2(n 4) ! H2 + H, significantly diminishing its importance in Saturn’s ionospheric photochemistry. Citation: Moore, L., A. F. Nagy, A. J. Kliore, I. Müller-Wodarg, J. D. Richardson, and M. Mendillo (2006), Cassini radio occultations of Saturn’s ionosphere: Model comparisons using a constant water flux, Geophys. Res. Lett., 33, L22202, doi:10.1029/2006GL027375.