Plasma Dynamics Observed Near Local Noon in Jupiter's Magnetosphere With the Galileo Spacecraft

During January 18-21, 2002, the Galileo spacecraft achieved a marvelous series of thermal plasma measurements in the local noon sector at Jovian radial distances in the range of about 10 to 50 R_J. Intense electron beams aligned along the magnetic field at two current sheet crossings by the spacecraft were found at radial distances of 24 and 29 R_J. These field lines thread the main auroral ring in Jupiter's atmosphere. The electron fluxes were detected at energies ranging from 3.7 to 14.8 keV and were sufficiently high to account for typical auroral luminosities. As the spacecraft moved outwards large departures from rigid corotational flow began at a radial distance of about 16 R_J. A stagnant region for flows was centered at about 26 R_J which was followed by a return of the plasma flows to nearly corotational values for the current sheet crossing at 29 R_J. Field-aligned heavy ions with M/Q = 16 and also protons were often observed at locations away from the position of the current sheet at Jovian radial distances in the range of about 18 to 32 R_J. These beams are examined in terms of their possible role in resolving questions of radial force balance in the outer magnetosphere. A remarkable feature of the ion densities in the local noon sector is a System III longitude effect at radial distances in the range of 32 to 44 R_J.