Waves and fluctuations in the jovian magnetosphere

The dynamics of the jovian magnetosphere are dominated by the mass loading of the Io torus. Sulfur dioxide and possibly other gases such as hydrogen are sputtered from Io and are ionized. These ions in turn are accelerated by the corotational electric field. The hot torus moves slowly outward and then ever more rapidly until reconnection releases the ions down the tail. The outward transport is far from steady. Near Io are intense ion cyclotron waves. As observed by Galileo these waves weakened rapidly on the side of Io closest to Jupiter. Beyond 10 Io radii (R-Io) at periods less than 150s there were no discernable waves above the instrument noise level. On the side of Io away from Jupiter the Io cyclotron waves disappeared at about 20 R-Io and the noise level in the torus reached values almost as low as those inside the Io orbit. However, as the radial distance increased so did the noise levels. The noise levels from 0.01 to 0.1 Hz are about 2 orders of magnitude greater at 7.7 R-J than inside the Io orbit at 5.5 R-J. The noise appears to be due to steps in the magnetic field strength and direction perhaps due to the interchange of tubes of flux with differing plasma content. The transverse power spectral density is greater than the compressional power in this region. The next region in which we have observations is the orbit of Europa and beyond. At frequencies of about 1 Hz the waves are more strongly compressional than transverse in the equatorial regions and more transverse than compressional off the equator. The outer edge of the dipolar region is about 24 R-J. The noise just inside this distance is quite variable from rotation to rotation. Outside this distance in the magnetodisk the field crossing the current sheet varies significantly from orbit to orbit as if the magnetodisk were globally unstable. Beyond about 40 R-J the location of the current sheet oscillates with a period of about 10 minutes. Beyond 50 R-J the plasma enters a regime of intermittent reconnection. (C) 2000 COSPAR. Published by Elsevier Science Ltd. All rights reserved.