Abstract
Abstract. On the basis of the spontaneous fast reconnection model, three-dimensional magnetic field profiles associated with a large-scale plasmoid propagating along the antiparallel magnetic fields are studied in the general sheared current sheet system. The plasmoid is generated ahead of the fast reconnection jet as a result of distinct compression of the magnetized plasma. Inside the plasmoid, the sheared (east-west) field component has the peak value at the plasmoid center located at x=XC, where the north-south field component changes its sign. The plasmoid center corresponds to the so-called contact discontinuity that bounds the reconnected field lines in x<XC and the field lines without reconnection in x>XC. Hence, contray to the conventional prediction, the reconnected sheared field lines in x<XC are not spiral or helical, since they cannot be topologically connected to the field lines in x>XC. It is demonstrated that the resulting profiles of magnetic field components inside the plasmoid are, in principle, consistent with satellite observations. In the ambient magnetic field region outside the plasmoid too, the magnetic field profiles are in good agreement with the well-known observations of traveling compression regions (TCRs).
Highlights
Magnetic reconnection is essential for large dissipative events in space plasmas, such as solar flares and geomagnetic substorms (Klimchuk, 2006; Nakamura et al, 2006; Sharma et al, 2008)
Ugai and Tsuda (1977) demonstrated for the first time that the fast reconnection mechanism can be realized in a 2-D current sheet system as an eventual solution of MHD if an anomalous resistivity is locally enhanced around an X neutral point
The underlying physics lies in the subsequent hydromagnetic stage, in which the resulting J × B force drives the plasma flow to effectively concentrate the current into the diffusion region
Summary
On the basis of Ugai and Tsuda (1977), we have proposed the spontaneous fast reconnection model and demonstrated by 2-D and three-dimensional (3-D) MHD simulations that the fast reconnection mechanism can be realized by a nonlinear instability due to the positive feedback between currentdriven anomalous resistivities and global reconnection flows (Ugai, 1984, 1992, 1999; Ugai and Zheng, 2005). In the 3D current sheet system without initial sheared field, the key physical condition for the fast reconnection evolution is that the current sheet width in the sheet current direction is about three times larger than its thickness (Ugai, 2008a, 2009b). In the presence of initial sheared field, the fast re- gion are the direct outcome of the plasmoid propagation, and connection evolution becomes harder for the larger sheared the TCR signatures can exactly be explained both qualitafield (Ugai, 2010a), and in a force-free current sheet the con- tively and quantitatively (Ugai and Zheng, 2006a, b). An essential question is to sheared fields are initially present both outside and inside clarify how a large-scale plasmoid is generated by magnetic the current sheet, whereas any magnetic flux closure across reconnection and propagates in the tail current sheet, and the the current sheet is not considered initially. It should be noted that Bx,By and Bz in the present coordinate system correspond to, respectively, −Bx,−Bz and −By in the conventional GSM coordinates (Fig. 1) (Ugai and Zheng, 2006a, b)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
