Rotational anisotropy of the Jovian magnetosphere at high latitudes

Abstract

The Ulysses spacecraft passed through the Jovian system in February 1992. Its trajectory, determined by its interplanetary mission, directed the spacecraft to the previously unexplored high‐latitude regions of the Jovian magnetosphere. Like Pioneers 10 and 11 and the two Voyagers, Ulysses entered the magnetosphere in the near equatorial morning sector, but unlike the previous spacecraft, Ulysses exited at high latitude near local dusk. This report considerably extends the work of Lanzerotti et al. (1993) by analyzing the extent of rotational anisotropy at high southern Jovigraphic latitudes attained by Ulysses during its outbound pass. Using data acquired by the Ulysses Heliosphere Instrument for Spectral, Composition, and Anisotropy at Low Energies (HI‐SCALE), we report some evidence of corotational flow in the high‐latitude duskside magnetosphere. On the inbound pass the Ulysses HI‐SCALE instrument observed anisotropies indicating partial corotation and a corotation lag. These data are consistent with Voyager plasma and energetic particle results. This is the first report of flow in the corotational direction from 44–57 RJ in the duskside, high‐latitude Jovian magnetosphere. There is strong evidence for a substantially reduced corotational anisotropy in this duskside region relative to a comparable radial distance range, 47–59 RJ, on the dayside.