Magnetic Reconnection in Sheared Solar Magnetic Arcades

The evolution of solar magnetic arcades is investigated with the use of MHD simulations imposing resistivity on sheared magnetic elds. It is found that there is a critical amount of shear, over which magnetic reconnection can take place in an arcade-like eld geometry to create a magnetic island. The process leading to reconnection cannot be solely attributed to a tearing instability, but rather to a reactive evolution of the magnetic arcade under resistivity. The natures of the arcade reconnection are governed by the spatial pattern of resistivity. A fast reconnection with a small shock angle can only be achieved when the diiusion region is localized. In this case, a highly collimated reconnection outtow can tear the plasmoid into a pair, and most of principal features in solar eruptive processes are reproduced.