Toroidal Flux Ropes Research Articles

A new paradigm for solar filament eruptions

This article discusses the formation, magnetic structure, and eruption of solar 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. According to this paradigm, filaments erupt when photospheric motions shear the fields, increasing their energy and decreasing their stability. According to a new paradigm, subsurface motions generate toroidal magnetic flux ropes, and after these flux ropes emerge to form active regions, the most twisted parts migrate into the corona to form filaments. Filaments become unstable and are ejected after a sufficient accumulation of twist (i.e., magnetic helicity). Various proposed mechanisms for producing the needed helicity are reviewed, and several observational tests are proposed to differentiate among the possible mechanisms.

November 17–18, 1975, event: A clue to an internal structure of magnetic clouds?

During November 17–18, 1975, a magnetic cloud was observed by the IMP 8 satellite. The cloud was analyzed in several papers. It draws attention because it is the most clear example where the magnetic field components behave differently from the current single flux rope model. Various models and fits have been presented to explain the magnetic field measurements for this particular event: single‐polarity cylindrical flux rope, spheromak, toroidal flux rope, and two subsequent flux ropes (flux rope twins). We critically examine these models and fits and stress that not only magnetic field data but also plasma data must be taken into account. There is a remarkably sharp drop in the density inside the magnetic cloud. The most consistent explanation of the behavior of magnetic field and plasma data for this event is that the magnetic cloud consists of a dual‐polarity flux rope with a low density and strong magnetic field core surrounded by an annular region of the same chirality but opposite polarity. An implication of this possibility to explain other magnetic cloud observations is discussed.