Solar flares - Magnetohydrodynamic instabilities

It is pointed out that most solar flares are either simple-loop (or compact) flares or two-ribbon flares. A single loop brightens and decays without moving, whereas the appearance of the two-ribbon type involves the eruption of a magnetic arcade. The present investigation is concerned with the basic MHD instabilities which may be responsible for the solar flares. A summary of some basic theoretical concepts is provided, taking into account the tearing-mode instability, magnetic reconnection, and the energy method. Three mechanisms for producing a simple-loop flares are discussed, giving attention to the kink instability, a thermal nonequilibrium, and the theory of the emerging flux model. It is found that a two-ribbon flare is probably caused by the instability of the sheared magnetic configuration in which a filament is situated.