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Signatures of field‐aligned currents in Saturn's nightside magnetosphere

We report first results of a survey of near‐simultaneous and near‐conjugate magnetic field perturbations observed over Saturn's northern and southern nightside auroral regions on ∼40 periapsis passes of the Cassini spacecraft during 2008. Structured azimuthal fields that are generally anti‐symmetric north and south were observed at auroral latitudes on all passes, indicative of the signatures of field‐aligned currents associated with magnetosphere‐ionosphere coupling. Two basic field patterns are discerned. One is associated exclusively with ‘lagging’ fields on high‐latitude field lines in both hemispheres, while the other includes a transition from ‘lagging’ to ‘leading’ fields with decreasing latitude in both hemispheres. The principal field‐aligned currents are found to span the region of the open‐closed field line boundary and the outer magnetosphere/ring current, with the region of upward current, potentially associated with ionospheric auroral emissions, usually being located on closed field lines just equatorward of the boundary.