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The upper ionospheres of Jupiter and Saturn
Authors:Tariq Majeed

John C McConnell

Institution:

Lunar and Planetary Laboratory, Gould-Simpson Building, University of Arizona, Tucson, AZ 85721, U.S.A.

Department of Earth and Atmospheric Science, York University, North York, Ontario, Canada M3J 1P3

Abstract:We use a 1-D chemical diffusive model, in conjunction with the measured neutral atmospheric structure, to analyze the Voyager RSS electron density, ne, profiles for the ionospheres of Jupiter and Saturn. As with previous studies we find serious difficulties in explaining the ne measurements. The model calculates ionospheres for both Jupiter and Saturn with ne peaks of not, vert, similar 10 times the measured peaks at altitudes which are not, vert, similar 900–1000 km lower than the altitude of peaks in the RSS electron densities. Based on our knowledge of neutral atmospheric structure, ionization sources, and known recombination mechanisms it seems that, vibrational excitation of H2 must play some role in the conversion of slowly radiatively recombining H+ ions to the relatively more rapidly recombining H2+ and H3+ ions. In addition, vertical ion flow induced by horizontal neutral winds or electric fields probably also play some role in maintaining the plasma peaks observed both for Jupiter and Saturn to be at high altitudes. For the ionosphere of Saturn, the electron densities are affected by a putative influx of H2O molecules, ΦH2O, from the rings. To reproduce the RSS V2 exit ne results model requires an influx of ΦH2O not, vert, similar 2 × 107 molecules cm−2 s−1 without invoking H2f vibrational excitation. To maintain the model ne peak at the measured altitude vertical plasma drift maintained by meridional winds or vertical electric fields is required. The amounts of H2O are consistent with earlier estimates of Connerney and Waite (1984) and do not violate any observational constraints.
Keywords:
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