Bifurcated current sheets produced by magnetic reconnection in the solar wind

Abstract

We report observations from the Wind spacecraft of Petschek‐like magnetic reconnection exhausts and thin current sheets in the solar wind on 19 and 20 November 2007, encompassing a solar wind disturbance driven by a magnetic cloud and followed by a corotating high‐speed stream. We have identified an unusually large number (11) of reconnection exhausts in this 2‐day interval using 3‐s plasma and magnetic field data. Despite the relatively smooth large‐scale field rotation associated with the magnetic cloud, five of the exhausts occurred within the cloud; three of those exhausts were associated with extremely small (<18°) local field shear angles. All 11 exhausts contained double‐step magnetic field rotations; such double‐step rotations are called bifurcated current sheets since they result from the splitting of reconnecting current sheets as an after‐effect of the reconnection process. We have also identified 27 current sheets in this 2‐day interval that were too thin to be adequately resolved by the 3‐s plasma measurement cadence. All of these thin current sheets were well resolved by the 92 ms magnetic field measurement. At least three, and possibly six, of these relatively thin current sheets had double‐step magnetic field rotations, indicating the underlying current sheets had probably been disrupted by magnetic reconnection. Current sheets thinner than ∼3 ion inertial lengths were not present in this data set. The relative lack of such ultrathin current sheets in the solar wind in general suggests that such current sheets usually are quickly disrupted by magnetic reconnection.