Three-dimensional evolution of the fast reconnection mechanism in a force-free current sheet

As a sequence of the recent paper on the fast reconnection evolution in a sheared current sheet [M. Ugai, Phys. Plasmas 17, 032313 (2010)], the present paper further studies the three-dimensional fast reconnection evolution in a force-free current sheet system. In general, for the larger sheared field magnitude, the fast reconnection evolution requires the larger spatial scales of the current sheet. For the force-free current sheet system, the critical condition for the fast reconnection evolution is that the current sheet width (extent) in the sheet current direction is about six times larger than its thickness. Once the fast reconnection evolves, the low-β plasma pressure is drastically enhanced in the reconnection outflow region to become comparable with the ambient magnetic pressure. Ahead of the Alfvénic fast reconnection jet, a large-scale plasmoid is formed, where the enhanced plasma pressure is stored. Inside the plasmoid, the sheared field lines are piled up in the form of a core and are significantly wound (or bent) in the sheared field (sheet current) direction because of the oblique plasmoid propagation along the sheared field. The resulting spatial changes in magnetic fields in the plasmoid are found to be in good agreement with the magnetic field signatures usually obtained by satellite observations inside the plasmoid propagating down in the geomagnetic tail.