Evolution of the current wedge and the generator current circuit by fast reconnection

Temporal dynamics of the generator current circuit and the current wedge is studied on the basis of the spontaneous fast reconnection model. Once the fast reconnection jet causes magnetic field dipolarization, a magnetohydrodynamic (MHD) generator arises ahead of the magnetic loop top. The generator effect is so powerful that a current circuit is strongly driven in the generator region and evolves to approach the loop footpoint through field-aligned currents along the loop boundary; simultaneously, the sheet current directed to the generator region turns its direction toward the loop footpoint, giving rise to current wedge evolution outside the generator current circuit. Both these current circuits are eventually connected to a layer around the separatrix in the loop footpoint, where the current is concentrated and intensified, leading to drastic energy dissipations. It is concluded that the MHD generator ahead of the magnetic loop top, provided and sustained by the fast reconnection jet, plays a crucial role in the two-ribbon heating observed in geomagentic substorms and solar flares.