A new paradigm for solar filament eruptions

This article discusses the formation, magnetic structure, and eruption of s olar filaments in terms of two contrasting paradigms. The standard paradigm is that filaments are formed by condensation of plasma on coronal magnetic fields that are twisted or dimpled as a result of photospheric motions. Ac cording to this paradigm, filaments erupt when photospheric motions shear t he fields, increasing their energy and decreasing their stability. Accordin g to a new paradigm, subsurface motions generate toroidal magnetic flux rop es, and after these flux ropes emerge to form active regions, the most twis ted parts migrate into the corona to form filaments. Filaments become unsta ble and are ejected after a sufficient accumulation of twist (i.e., magneti c helicity). Various proposed mechanisms for producing the needed helicity are reviewed, and several observational tests are proposed to differentiate among the possible mechanisms.