Stability of prominences exposing helical-like patterns

Abstract

The internal structure of prominences appearing as twisted tubes was studied. The sample embraced 15 stable and 13 eruptive prominences, exposing patterns which possibly reflect a helical configuration. The equivalent pitch angles (0) of twisted fine structure features were measured. In some cases the evolution of the internal structure was followed and 49 independent measurements of the parameter were performed in total The results are presented in the plane relating the parameter ~9 and the normalized prominence height. The eruptive prominences occupy the region characterized by 0 > 50 ~ and h > 0.8d, where h and d are the prominence height and the footpoint half-separation, respectively. All prominences characterized by h < 0.6d or by 0 < 35 ~ were stable. Such a result is in good agreement with an order of magnitude treatment of the forces acting in a curved magnetic tube, anchored at both ends in the photosphere.

Structure, Stability, and Evolution of Magnetic Flux Ropes From the Perspective of Magnetic Twist

“…First of all, eruptive structures with a clear writhing feature are relatively rare, which raises a question as to how often the kink instability triggers eruptions. Second, twisted, helical patterns are often exposed only during eruptions (e.g., Vrsnak et al 1991Vrsnak et al , 1993Romano et al 2003;Gary & Moore 2004;Srivastava et al 2010;Kumar et al 2012). It is hence difficult to determine whether the twist is accumulated prior to the eruption or built up in the course of the eruption through reconnection in the vertical current sheet under the rope (Lin et al 2003).…”

Experimental Identification of the Kink Instability as a Poloidal Flux Amplification Mechanism for Coaxial Gun Spheromak Formation

“…This Letter experimentally identifies the MHD kink instability [7] as a 3D mechanism which converts toroidal to poloidal flux in a coaxial gun system, thereby leading to spheromak formation. This mechanism should also be of fundamental importance to coaxial helicity injection in spherical tori [8], relaxation in reversed-field pinches [4], solar coronal plasma instabilities [9], and astrophysical jets [10].Plasmas in this experiment fall into three regimes depending on peak λ gun = µ 0 I gun /ψ gun (where I gun is the gun current and ψ gun is the bias poloidal magnetic flux intercepting the inner gun electrode), with (I) low values resulting in a straight plasma column with helical magnetic field along the symmetry axis, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma with B tor ≫ B pol . Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit [7], and the kink acts as a dynamo which converts toroidal to poloidal flux.…”

Quiescent Solar Prominences and Magnetic‐Energy Storage

“…Copious drainage of H is commonly observed in prominence eruptions (Lipscy 1998;Tandberg-Hanssen 1995;Rusin & Rybansky 1982;Vsrnak 1998;Vsrnak et al 1991). The lightening of an initially heavy prominence results naturally in an overcompensating Lorentz force to drive the local magnetic structure out of the corona.…”

“…The lengthy ones in the high latitudes near the boundaries of polar coronal holes are typically of the inverse type. Observations and theory suggest that inverse prominences are condensations inside a larger scale flux rope of twisted magnetic fields in the corona, whose central length is not magnetically connected to the photosphere directly below (Amari & Aly 1992;Aulanier & Demoulin 1998;Chen 1989;Chen et al 1997;Ciaravella et al 2000;Dere et al 1999;Gilbert et al 2000Gilbert et al , 2001Lites & Low 1997;Low 1993Low , 1999aPriest, Hood, & Anzer 1989;Rust & Kumar 1994;Schonfelder & Hood 1995;Tandberg-Hanssen 1995;Vsrnak 1998;Vsrnak, Ruzdjak, & Rompolt 1991;Wu et al 1997). Normal prominences are associated with active regions, and it has been suggested that they tend to form early in the history of an active region (Zhang & Low 2001;Low & Zhang 2002) In this paper, we study quiescent prominences as hydromagnetic structures on coronal scales over which the inverse-square decline of gravity and the curvature of the solar surface are important.…”