Abstract
AbstractPetschek‐type reconnection is expected to result in bifurcations of reconnection current sheets. In contrast, Hall reconnection simulations show smooth changes in the reconnecting magnetic field. Here we study three solar wind reconnection events where different spacecraft sample oppositely directed reconnection exhausts from a common reconnection site. The spacecraft's relative separations and measurements of the exhaust width are used to geometrically calculate each spacecraft's distance from the X line. We find that in all cases spacecraft farthest from the X line observe clearly bifurcated reconnection current sheets, while spacecraft nearer to the X line do not. These observations suggest that clear bifurcations of reconnection current sheets occur at large distances from the X line (~1000 ion skin depths) and that Petschek‐type signatures are less developed close to the reconnection site. This may imply that fully developed bifurcations of reconnection current sheets are unlikely to be observed in the near‐Earth magnetotail.
Highlights
The process of magnetic reconnection changes the magnetic topology within plasmas and converts magnetic energy into thermal and kinetic energy
Petschek [1964] proposed that the reconnection rate could be enhanced for antiparallel reconnection if the diffusion region was reduced in size and if the majority of plasma passed through slow-mode shocks along the edges of two oppositely directed exhausts of accelerated plasma outflow
We find that the spacecraft farthest from the reconnection site observes a clearly bifurcated current sheet in agreement with Petschek-type reconnection, whereas spacecraft closer to the reconnection site do not
Summary
The process of magnetic reconnection changes the magnetic topology within plasmas and converts magnetic energy into thermal and kinetic energy. Liu et al [2012] showed that in a large-scale 2.5-D PIC simulation of antiparallel reconnection large ion temperature anisotropies develop and push the exhaust toward becoming firehose unstable, preventing the formation of slow shocks and current sheet bifurcations Such large anisotropy has been observed for near-antiparallel reconnection in the magnetotail [Hietala et al, 2015]. We study the magnetic structure of three rare reconnection observations where different spacecraft observe oppositely directed solar wind exhausts from a common reconnection site As both sides of the X line were observed, we can use constraints from spacecraft observations to estimate each spacecraft’s distance from the X line in the outflow direction and the implied reconnection rate. This allows, for the first time, observational constraints to be placed on the distance from the X line at which bifurcations of reconnection current sheets may form
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