Plasmoid-induced-reconnection and fractal reconnection

As a key to undertanding the basic mechanism for fast reconnection in solar flares. plasmoid-induced-reconnection and fractal reconnection are propose d and examined. We first briefly summarize recent solar observations that g ive us hints on the role of plasmoid (flux rope) ejections in flare energy release. We then discuss the plasmoid-induced-reconnection model, which is an extention of the classical two-ribbon-flare model which we refer to as t he CSHKP model. An essential ingredient of the new model is the formation a nd ejection of a plasmoid which play an essential role in the storage of ma gnetic energy (by inhibiting reconnection) and the induction of a strong in flow into reconnection region. Using a simple analytical model, we show tha t the plasmoid ejection and acceleration are closely coupled with the recon nection process, leading to a nonlinear instability for the whole dynamics that determines the macroscopic reconnection rate uniquely. Next we show th at the current sheet tends to have a fractal structure via the following pr ocess path: tearing double right arrow sheet thinning double right arrow Sw eet-Parker sheet double right arrow secondary tearing double right arrow fu rther sheet thinning double right arrow (...). These processes occur repeat edly at smaller scales until a microscopic plasma scale (either the ion Lar mor radius or the ion inertial length) is reached where anomalous resistivi ty or collisionless reconnection can occur. The current sheet eventually ha s a fractal structure with many plasmoids (magnetic islands) of different s izes. When these plasmoids are ejected out of the current sheets, fast reco nnection occurs at various different scales in a highly time dependent mann er. Finally, a scenario is presented for fast reconnection in the solar cor ona on the basis of above plasmoid-induced-reconnection in a fractal curren t sheet.