Plasmoid Formation in Eruptive Flares

Abstract

Mass eruptions are often associated with solar flares, which are sometimes called plasmoid eruptions or filament eruptions (observed in Hα). Theo-retically, these eruptive phenomena have been considered to be related to an instability or a loss of equiHbrium of the coronal magnetic field. Since the magnetic force is much stronger than both the gas pressure and the gravity force in the corona, coronal structures are mainly controlled by the magnetic field. Therefore, unless a magnetically-driven event occurs, the coronal structures evolve in a series of quasi-static states, but once an instability develops or a loss of equilibrium is achieved, they no longer stay in a static state and enter on a dynamical stage. This scenario has made it important to study the stabilities and natures of the equilibrium configurations of the coronal magnetic field. Recently, the rapid develop-ment of computers has enabled us to trace the temporal evolution of the coronal magnetic field directly by means of numerical simulations. Such work is found in, e.g., Mikic, Barnes, and Schnack (1988), Biskamp and Welter (1989), Finn, Guzdar, and Chen (1992), Inhester, Birn, and Hesse (1992), and Choe (1995). These papers studied how the coronal magnetic field evolved under situations where shearing or converging motion was imposed in the photosphere.