Momentum transfer between the Io plasma wake and Jupiter's ionosphere

[1] The interaction between Io and Jupiter is dramatically illustrated by recent ultraviolet and infrared imaging of Jupiter's ionosphere. Bright auroral emissions are observed at the base of Io's flux tube with emissions at the footprint of Io's wake extending large distances downstream ( roughly 100degrees around Jupiter). We propose as a possible explanation for the persisting wake emissions a subcorotating torus flux tube downstream from Io that results in high-latitude parallel electric fields. The transfer of momentum to the subcorotating Iogenic plasma from first the corotating torus and eventually the Jovian ionosphere via the Alfvenic interaction result in intense field-aligned currents which can lead to the formation of parallel electric fields. By comparing the field-aligned current density of the initial Alfvenic disturbance generated by the stagnated flow in Io's wake to the required current density for steady state acceleration of the flux tube we infer a current limitation, or momentum decoupling, caused by a high-latitude field-aligned potential drop. As a result, the subcorotating flux tube is partially decoupled from the Jovian ionosphere and auroral emissions persist for large distances downstream of the initial Io-disturbed flux tube. Model results suggest that the extended wake emissions are initially driven by a similar to70 kV cross-wake potential, which is consistent with observed auroral emissions caused by electron precipitation with energy on the order of tens of keV.