Abstract
Abstract. The fast reconnection mechanism, involving slow shocks and Alfvénic fast plasma jets, is most responsible for the explosive conversion of magnetic energy associated with geomagnetic substorms and solar flares. In this paper, the spontaneous fast reconnection model is applied to well-known phenomena of substorms. When the east-west width of the tail current sheet becomes 3–4 times larger than its north-south thickness, the fast reconnection mechanism can fully be established, which may lead to substorm onset. The resulting Alfvénic jet can exactly explain, both qualitatively and quantitatively, the in-situ satellite observations of the traveling compression regions (TCRs) associated with large-scale plasmoids propagating down the tail. Also, the earthward fast reconnection jet causes drastic magnetic field dipolarization, so that the sheet current ahead of the magnetic loop of closed field lines suddenly turns its direction toward the loop footpoint and a large-scale current wedge is formed according to the growth of field-aligned currents. It is demonstrated that an MHD generator arises ahead of the magnetic loop and drives the current wedge to distinctly enhance the current density in a pair of thin layers of the loop footpoint, giving rise to drastic heating in the form of two ribbons.
Highlights
The fast reconnection mechanism, involving Alfvenic plasma jets, must be most responsible for flare phenomena in space plasmas (Shibata, 1999; Sharma et al, 2008)
We have proposed the spontaneous fast reconnection model and demonstrated by 2-D and three-dimensional (3-D) simulations that the fast reconnection mechanism can be realized as an eventual solution of MHD equations by the nonlinear instability due to positive feedback between current-driven anomalous resistivities and global reconnection flows (Ugai, 1984, 1999; Ugai and Zheng, 2005)
We find that when the fast reconnection jet collides with the magnetic loop of closed field lines, field-aligned currents suddenly appear because of drastic increase in the sheared field Bz inside the loop, leading to drastic evolution of the current wedge
Summary
The fast reconnection mechanism, involving Alfvenic plasma jets, must be most responsible for flare phenomena in space plasmas (Shibata, 1999; Sharma et al, 2008). Many MHD models have assumed explicit resistivity models, such as current-driven anomalous resistivities, in 3-D (Raeder, 2003; Isobe et al, 2005) and 2-D (Uzdensky, 2003; Klimas et al, 2004; Yokoyama and Shibata, 1994) situations. These studies have shown that if the resistivity is enhanced locally around an X point, magnetic reconnection occurs effectively, which is consistent with our results.
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