Jovian Cusp Processes: Implications for the Polar Aurora

Jupiter's polar emissions, which include all auroral emission lying poleward of the main auroral oval, are ordered by magnetic local time, indicating external control by the solar wind interaction with the jovian magnetosphere. The main auroral oval itself appears fixed with respect to the planet, an indication of planetary control, and is understood to be associated with magnetosphere-ionosphere coupling, and the transfer of angular momentum from the ionosphere to the middle magnetosphere plasma. We have recently considered the flows present in Jupiter's ionosphere in terms of three different regimes: the sub-corotational flows associated with the main auroral oval, the Vasyliunas cycle associated with the down-tail loss of plasmoids (predominantly a feature of the dusk-side magnetosphere), and the Dungey-cycle flows which are associated with the interaction of the solar wind and embedded interplanetary magnetic field with the magnetosphere, principally via reconnection. Motivated by this picture, we consider from a theoretical standpoint what the effects of pulsed dayside magnetic reconnection will be at Jupiter. This will generate a twin-vortical flow pattern in the ionosphere across the open-closed field line boundary, associated with a bi-polar (i.e. upward and downward) field-aligned current pair. These currents will be of order ∼1-2 MA, representing <10% of the magnetopause current, flowing in a region ~1000 km across at ionospheric heights, such that the field-aligned current densities peak at ∼1 μ A m^-2. Here we investigate the conditions under which such currents may be carried in either magnetospheric or cusp plasmas, and consider the consequences for auroral emissions at UV and X-ray wavelengths.