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 hecto‐decameter 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 arc 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.