Sustained lobe reconnection in Saturn’s magnetotail

The degree to which solar wind driving may affect Saturn’s magnetosphere is not yet fully understood. We present observations that suggest that under some conditions the solar wind does govern the character of the plasma sheet in Saturn’s outer magnetosphere. On 16 September 2006, the Cassini spacecraft, at a radial distance of 37 Rs near local midnight, observed a sunward flowing ion population for ~5 h, which was accompanied by enhanced Saturn Kilometric Radiation emissions. We interpret this beam as the outflow from a long‐lasting episode of Dungey‐type reconnection, i.e., reconnection of previously open flux containing magnetosheath material. The beam occurred in the middle of a several‐day interval of SKR activity and enhanced lobe magnetic field strength, apparently caused by the arrival of a solar wind compression region with significantly higher than average dynamic pressure. The arrival of the high‐pressure solar wind also marked a change in the composition of the plasma‐sheet plasma, from water‐group‐dominated material clearly of inner‐magnetosphere origin to material dominated by light‐ion composition, consistent with captured magnetosheath plasma. This event suggests that under the influence of prolonged high solar wind dynamic pressure, the tail plasma sheet, which normally consists of inner‐magnetospheric plasma, is eroded away by ongoing reconnection that then involves open lobe field lines. This process removes open magnetic flux from the lobes and creates a more Earth‐like, Dungey‐style outer plasma sheet dominantly of solar wind origin. This behavior is potentially a recurrent phenomenon driven by repeating high‐pressure streams (corotating interaction regions) in the solar wind, which also drive geomagnetic storms at Earth.Key PointsEvidence for long‐lasting Dungey‐type magnetotail reconnection at Saturn is presentedThis event is associated with arrival of a solar wind stream‐driven compression regionCreation of a more Earth‐like outer plasma sheet may be a recurrent stream‐driven phenomenonPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134869/1/jgra52237.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134869/2/jgra52237_am.pd