A simple empirical model of the equatorial radial field in Jupiter's middle magnetosphere, based on spacecraft fly-by and Galileo orbiter data

Details A simple empirical model of the equatorial radial field in Jupiter's middle magnetosphere, based on spacecraft fly-by and Galileo orbiter data A simple empirical model of the equatorial radial field in Jupiter's middle magnetosphere, based on spacecraft fly-by and Galileo orbiter data

Jun 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002p%26ss...50..789b&link_type=abstract

Planetary and Space Science, Volume 50, Issue 7-8, p. 789-806.

Computer Science

3

Scientific paper

In this paper we consider empirical models of the radial field and azimuthal current in Jupiter's middle magnetosphere region, at distances in the range 20-45RJ. We first of all compare the model derived previously by Bunce and Cowley (Planet. Space Sci. 49 (2001) 261) using Pioneer, Voyager and Ulysses fly-by data, with a combined data set that now also incorporates data from the first twenty orbits of the Galileo orbiter. The overall RMS fractional residual is found to be 12.7%, such that the model does provide a good description of the combined data set. In particular, it is shown that the Galileo data also exhibit the same local time asymmetry as found in the fly-by data, in which the radial field (and azimuthal current) are stronger at a given radial distance on the nightside compared with the dayside. However, it is also shown that if the combined data are separated into 2h bins of local time and then fitted to individual power law curves, the overall RMS fractional residual is reduced to 7.7%, thus showing scope for improvement in the empirical model. Based on the combined data set, in our revised model the field is taken as asymmetric outside of 14.5RJ, and to fall with radial distance with an exponent which is taken to vary sinusoidally with local time, varying between /-1.5 at noon and /-1.0 at midnight, such that the field becomes increasingly asymmetric with increasing distance. The overall RMS residual for this four-parameter model is found to be 9.7%, only slightly higher than that of the free-fits to the 2h MLT binned data, and representing a worthwhile improvement over the original Bunce and Cowley model. The implied divergence of the azimuthal current for the revised model peaks at ~15kARJ-2 near the dawn-dusk meridian at a radial distance of ~23RJ. The implied difference in the total azimuthal current flowing in the current sheet between 20 and 50RJ at midnight compared with noon is 19MA, in a total (at dawn and dusk) of 59MA.

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