AN INTERPRETATION OF THE BROAD-BAND VLF WAVES NEAR THE IO TORUS AS OBSERVED BY ULYSSES

The requirements for the Ulysses trajectory to attain high ecliptic la titudes using a Jovian gravitational assist resulted in a fortuitous p assage through the Io torus region. Specifically, the spacecraft spent many hours at latitudes just above the torus. During this time the lo w-frequency cutoff of an ordinary mode (O mode) emission allowed a det ermination of the local electron plasma frequency (i.e., electron dens ity) along the northern flank of the torus. Also, near a Jovian System III longitude of 100-degrees, the spacecraft flew past a set of activ e field lines that have been previously identified to be associated wi th the hectometric generation region. During the passage, Ulysses obse rved a newly discovered O mode component and a whistler mode emission similar to that observed by Voyager 1 13 years previously. All of the broadband VLF emissions imply the presence of a particular population of electrons. We suggest that broadband VLF emissions can be used as a ''particle detector'' to qualitatively measure the electron plasma co nditions in the torus region and identify active regions.