Sheared magnetic field structure in Jupiter's dusk magnetosphere: Implications for return currents

The configuration of the magnetic field near 100 R J in the dusk sector of the Jovian magnetosphere varies with distance from the equatorial current sheet. The changing twist out of meridian planes is consistent with flows that lag corotation near the equator but that may lead corotation at higher latitudes. Although a portion of the field perturbation may be produced by magnetopause currents, we argue that the observed sheared field structure requires field‐aligned current flowing toward Jupiter's ionosphere inside the magnetopause but beyond ∼100 R J . This current must include a portion of the return current of the system that enforces partial corotation of outward moving magnetospheric plasma and may also be fed by boundary layer currents of the region 1 type. We estimate the total current into the auroral ionosphere as ∼6 MA, and this current would flow into a narrow band of latitude (<2°) poleward of the main auroral oval.