Modeling of Io-Jupiter decameter arcs, emission beaming and energy source

Abstract

The electrodynamic interaction between Io and Jupiter causes electron acceleration in/near the Io flux tube (IFT), which in turn produces intense radio emissions in the hectodecameter range, displaying arc shapes in the time-frequency plane. The shapes depend on the hemisphere of origin of the emission and on the Io-Jupiter-observer geometry. Assuming radio wave generation by the cyclotron-maser instability, we simulate t-f are shapes as a function of emission beaming, lead angle between the radio emitting field line and the instantaneous Io field line, and electron energy. A good fit of arcs t-f location and shape is obtained for loss-cone driven (oblique) emission beamed in a hollow cone of half-angle ≥80° around the source magnetic field, closing at high frequencies, and of cone thickness ≤1°. The lead angle is found between a few degrees and ∼40° in both hemispheres. Resonant electron energies are about a few keV Implications on the absence of a plasma cavity at IFT footprints and on Jupiter's internal magnetic field model are discussed. Copyright 2008 by the American Geophysical Union.