COMPUTER STUDIES ON PLASMOID DYNAMICS ASSOCIATED WITH THE SPONTANEOUS FAST RECONNECTION MECHANISM

The spontaneous fast reconnection model is applied to the plasmoid dynamics, and computer simulations are performed for a wide range of parameters. According to the fast reconnection development, the resulting strong (Alfvenic) plasma jet drives a large-scale plasmoid to swell and propagate. Once the plasmoid fully develops, the propagation speed V-p becomes almost constant. It is the JxB force, not the pressure-gradient force, that plays the dominant role on the plasmoid propagation. It is estimated that V-p similar to 0.8 V-A (l0), where V-A (l0) is the Alfven velocity measured in the magnetic field region ahead of the plasmoid. Along the backward-half plasmoid boundary a strong slow (almost switch-off) shock is formed, whereas along the forward-half boundary a rather weak slow shock stands. The plasma pressure is largely enhanced in the middle of the plasmoid, and the magnetic energy just outside the plasmoid is notably enhanced in the forward half because of the generator effect and is then distinctly reduced in the backward half by the strong motor effect. For the uniform resistivity model, any distinct plasmoid cannot be set up. It is argued that the spontaneous fast reconnection mechanism should be most applicable to catastrophic events observed in space plasmas. (C) 1995 American Institute of Physics.