Magnetic disconnection from the Sun: Observations of a reconnection exhaust in the solar wind at the heliospheric current sheet

We have identified an anti-sunward-directed, Petschek-type, reconnection exhaust during a crossing of the heliospheric current sheet, HCS, by the ACE spacecraft. The exhaust in this relatively rare HCS event was a region of accelerated plasma flow filling the field reversal region and was bounded by Alfven waves propagating in opposite directions along recently merged field lines. Heliospheric magnetic field lines disconnected from the Sun by the reconnection process were identified in and surrounding the exhaust by the disappearance of the solar wind electron strahl there and by the interpenetration along the field of sunward-streaming halo electrons from opposite sides of the exhaust. These observations demonstrate that strahl dropouts observed in the vicinity of the HCS at least at times are signatures of magnetic disconnection from the Sun.