Equatorial electron beams and auroral structuring at Jupiter

Abstract

It has been reported that low-altitude regions of downward electric current on auroral magnetic field lines are sites of dramatic upward magnetic field-aligned electron acceleration that generates intense magnetic field-aligned electron beams within Earth's equatorial middle magnetosphere. Field-aligned equatorial electron beams also are observed within Jupiter's middle magnetosphere. The mystery about these Jovian beams is that they are observed in a region thought to map to Jupiter's brightest aurora and on field lines that generally carry electric current away from Jupiter's atmosphere rather than toward the atmosphere as anticipated at Earth. Here we develop procedures for quantifying the character of the Jupiter electron beams (for example, how confined they are with respect to the magnetic field-aligned directions). We apply the procedures to the highest time resolution electron data available from the Galileo Energetic Particle Detector (EPD). We find that the Jupiter equatorial electron beams are spatially and/or temporally structured (down to <20 km at auroral altitudes, or less than several minutes), with regions of intense beams intermixed with regions absent of such beams. We suggest that, as with the situation at Earth, Jupiter's circuit of electric currents that supports its brightest aurora is structured, with regions of upward current intermixed with regions of downward current. Copyright 2007 by the American Geophysical Union.