TY - JOUR A1 - Toeroek, T. A1 - Leake, J. E. A1 - Titov, Viacheslav S. A1 - Archontis, V. A1 - Mikic, Z. A1 - Linton, M. G. A1 - Dalmasse, K. A1 - Aulanier, Guillaume A1 - Kliem, Bernhard T1 - Distribution of electric currents in solar active regions JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters KW - magnetohydrodynamics (MHD) KW - Sun: corona KW - Sun: coronal mass ejections (CMEs) Y1 - 2014 U6 - https://doi.org/10.1088/2041-8205/782/1/L10 SN - 2041-8205 SN - 2041-8213 VL - 782 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Kliem, Bernhard A1 - Lin, J. A1 - Forbes, T. G. A1 - Priest, E. R. A1 - Toeroek, T. T1 - Catastrophe versus instability for the eruption of a toroadal solar magnetic flux JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The onset of a solar eruption is formulated here as either a magnetic catastrophe or as an instability. Both start with the same equation of force balance governing the underlying equilibria. Using a toroidal flux rope in an external bipolar or quadrupolar field as a model for the current-carrying flux, we demonstrate the occurrence of a fold catastrophe by loss of equilibrium for several representative evolutionary sequences in the stable domain of parameter space. We verify that this catastrophe and the torus instability occur at the same point; they are thus equivalent descriptions for the onset condition of solar eruptions. KW - magnetohydrodynamics (MHD) KW - Sun: corona KW - Sun: coronal mass ejections (CMEs) KW - Sun: filaments, prominences KW - Sun: flares KW - Sun: magnetic fields Y1 - 2014 U6 - https://doi.org/10.1088/0004-637X/789/1/46 SN - 0004-637X SN - 1538-4357 VL - 789 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Toeroek, T. A1 - Kliem, Bernhard A1 - Berger, M. A. A1 - Linton, M. G. A1 - Demoulin, P. A1 - van Driel-Gesztelyi, L. T1 - The evolution of writhe in kink-unstable flux ropes and erupting filaments JF - Plasma physics and controlled fusion N2 - The helical kink instability of a twisted magnetic flux tube has been suggested as a trigger mechanism for solar filament eruptions and coronal mass ejections (CMEs). In order to investigate if estimations of the pre-emptive twist can be obtained from observations of writhe in such events, we quantitatively analyze the conversion of twist into writhe in the course of the instability, using numerical simulations. We consider the line tied, cylindrically symmetric Gold-Hoyle flux rope model and measure the writhe using the formulae by Berger and Prior which express the quantity as a single integral in space. We find that the amount of twist converted into writhe does not simply scale with the initial flux rope twist, but depends mainly on the growth rates of the instability eigenmodes of higher longitudinal order than the basic mode. The saturation levels of the writhe, as well as the shapes of the kinked flux ropes, are very similar for considerable ranges of initial flux rope twists, which essentially precludes estimations of pre-eruptive twist from measurements of writhe. However, our simulations suggest an upper twist limit of similar to 6 pi for the majority of filaments prior to their eruption. KW - magnetohydrodynamics (MHD) KW - Sun: corona KW - Sun: filaments Y1 - 2014 U6 - https://doi.org/10.1088/0741-3335/56/6/064012 SN - 0741-3335 SN - 1361-6587 VL - 56 IS - 6 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - van Driel-Gesztelyi, L. A1 - Baker, Daniel N. A1 - Toeroek, T. A1 - Pariat, E. A1 - Green, L. M. A1 - Williams, D. R. A1 - Carlyle, J. A1 - Valori, G. A1 - Demoulin, P. A1 - Kliem, Bernhard A1 - Long, D. M. A1 - Matthews, S. A. A1 - Malherbe, J. -M. T1 - Coronal magnetic reconnection driven by CME expansion-the 2011 June 7 event JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent active regions during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube at the interface between the CME and the neighboring AR 11227. Reconnection resulted in the formation of new magnetic connections between the erupting magnetic structure from AR 11226 and the neighboring active region AR 11227 about 200 Mm from the eruption site. The onset of reconnection first becomes apparent in the SDO/AIA images when filament plasma, originally contained within the erupting flux rope, is redirected toward remote areas in AR 11227, tracing the change of large-scale magnetic connectivity. The location of the coronal reconnection region becomes bright and directly observable at SDO/AIA wavelengths, owing to the presence of down-flowing cool, dense (1010 cm(-3)) filament plasma in its vicinity. The high-density plasma around the reconnection region is heated to coronal temperatures, presumably by slow-mode shocks and Coulomb collisions. These results provide the first direct observational evidence that CMEs reconnect with surrounding magnetic structures, leading to a large-scale reconfiguration of the coronal magnetic field. KW - magnetic reconnection KW - magnetohydrodynamics (MHD) KW - Sun: corona KW - Sun: coronal mass ejections (CMEs) KW - Sun: magnetic fields KW - Sun: UV radiation Y1 - 2014 U6 - https://doi.org/10.1088/0004-637X/788/1/85 SN - 0004-637X SN - 1538-4357 VL - 788 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER -