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dc.contributor.authorFuentes-Fernández, Jorge
dc.contributor.authorParnell, Clare Elizabeth
dc.contributor.authorHood, Alan William
dc.identifier.citationFuentes-Fernández , J , Parnell , C E & Hood , A W 2011 , ' Magnetohydodynamics dynamical relaxation of coronal magnetic fields : II. 2D Magnetic X-Points ' , Astronomy & Astrophysics , vol. 536 , A32 .
dc.identifier.otherPURE: 66347361
dc.identifier.otherPURE UUID: c2e22e64-191c-426a-a92e-6e6b088f6e2f
dc.identifier.otherScopus: 82955189734
dc.identifier.otherORCID: /0000-0003-2620-2068/work/58055235
dc.identifier.otherORCID: /0000-0002-5694-9069/work/73700752
dc.description.abstractContext. Magnetic neutral points are potential locations for energy conversion in the solar corona. 2D X-points have been widely studied in the past, but only a few of those studies have taken finite plasma beta effects into consideration, and none of them look at the dynamical evolution of the system. At the moment there exists no description of the formation of a non-force-free equilibrium around a two-dimensional X-point. Aims. Our aim is to provide a valid magnetohydrostatic equilibrium from the collapse of a 2D X-point in the presence of a finite plasma pressure, in which the current density is not simply concentrated in an infinitesimally thin, one-dimensional current sheet, as found in force-free solutions. In particular, we wish to determine if a finite pressure current sheet will still involve a singular current, and if so, what is the nature of the singularity. Methods. We use a full MHD code, with the resistivity set to zero, so that reconnection is not allowed, to run a series of experiments in which an X-point is perturbed and then is allowed to relax towards an equilibrium, via real, viscous damping forces. Changes to the magnitude of the perturbation and the initial plasma pressure are investigated systematically. Results. The final state found in our experiments is a “quasi-static” equilibrium where the viscous relaxation has completely ended, but the peak current density at the null increases very slowly following an asymptotic regime towards an infinite time singularity. Using a high grid resolution allows us to resolve the current structures in this state both in width and length. In comparison with the well known pressureless studies, the system does not evolve towards a thin current sheet, but concentrates the current at the null and the separatrices. The growth rate of the singularity is found to be tD, with 0 < D < 1. This rate depends directly on the initial plasma pressure, and decreases as the pressure is increased. At the end of our study, we present an analytical description of the system in a quasi-static non-singular equilibrium at a given time, in which a finite thick current layer has formed at the null. The dynamical evolution of the system and the dependence of the final state on the initial plasma and magnetic quantities is discussed, as are the energetic consequences.
dc.relation.ispartofAstronomy & Astrophysicsen
dc.rights© ESO, 2011.en
dc.subjectMagnetohydrodynamic (MHD)en
dc.subjectMagnetic topologyen
dc.subjectMagnetic reconnectionen
dc.subjectQB Astronomyen
dc.subjectQC Physicsen
dc.titleMagnetohydodynamics dynamical relaxation of coronal magnetic fields : II. 2D Magnetic X-Pointsen
dc.typeJournal articleen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews.Applied Mathematicsen
dc.description.statusPeer revieweden

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