Wind observations of asymmetric magnetic reconnection in the distant magnetotail

Abstract

On February 23, 2001, during southward and strongly dawnward IMF, Wind traversed the distant magnetotail near XGSM = −90 RE. Wind encountered the mantle in the southern hemisphere and a nearly empty lobe in the northern hemisphere. In the current layer (plasma sheet), high‐speed tailward plasma jets with plasma density intermediate between the mantle and the lobe were detected. The speed of these flows were 96–99% of the Alfvén speed measured in the deHoffmann‐Teller frame. We interpret these observations as evidence for asymmetric reconnection involving a rotational discontinuity in the distant tail when the density in the two inflow regions are vastly different. This is in contrast to typical symmetric magnetotail reconnection involving two lobes of equal density where the flow acceleration across the slow shock is usually sub‐Alfvénic and the outflow density is enhanced relative to the inflow density. Hall effects are also observed in this event.