Remote sensing of possible plasma density bubbles in the inner Jovian dayside magnetosphere

Abstract

During the 2001 Cassini encounter with Jupiter, the Radio and Plasma Wave Science (RPWS) instrument detected fine spectral and temporal structure with broadband kilometric radiation. Applying known electron cyclotron harmonic radiation models, this microstructure is interpreted as originating from a plasma density depletion or bubble at the edge of the Io torus. The microstructure became very complicated at the event beginning and end (formation of broadband bursty structures), and this is interpreted as originating from high-frequency (3-4 s period) density waves or fingers found at the edge of the larger density bubble. Such high-frequency structure at the edges of plasma bubbles is reminiscent of small-scale structure associated with terrestrial spread-F density irregularities. We suggest that the narrow extended fingers, observed on a convex portion of the Io torus surface, result from the interchange instability that is shredding the outer edges of the plasma bubble. A similar set of circumstances occurring on a larger scale may explain the emission of Jovian radio bull's-eye emission observed previously by Ulysses.