Io‐related Jovian auroral arcs: Modeling parallel electric fields

Recent observations of auroral arcs on Jupiter suggest that electrons are being accelerated downstream from Io's magnetic footprint, creating detectable emissions. The downstream electron acceleration is investigated using one‐dimensional spatial, two‐dimensional velocity static Vlasov solutions under the constraint of quasi‐neutrality and an applied potential drop. The code determines self‐consistent charged particle distributions and potential structure along a magnetic field flux tube in the upward (with respect to Jupiter) current region of Io's wake. The boundaries of the flux tube are the Io torus on one end and Jupiter's ionosphere on the other. The results indicate that localized electric potential drops tend to form at 1.5–2.5 R J Jovicentric distance. A sufficiently high secondary electron density causes an auroral cavity to be produced similar to that on Earth. Interestingly, the model results suggest that the proton and the hot electron population in the Io torus control the electron current densities between the Io torus and Jupiter and thus may control the energy flux and the brightness of the aurora downstream from Io's magnetic footprint. The parallel electric fields also are expected to create an unstable horseshoe electron distribution inside the auroral cavity, which may lead to the shell electron cyclotron maser instability. Results from our model suggest that in spite of the differing boundary conditions and the large centrifugal potentials at Jupiter, the auroral cavity formation may be similar to that of the Earth and that parallel electric fields may be the source mechanism of Io‐controlled decametric radio emissions.