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, Pascal 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 - 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 - Cheng, X. A1 - Ding, M. D. A1 - Zhang, J. A1 - Sun, X. D. A1 - Guo, Y. A1 - Wang, Yi-Ming A1 - Kliem, Bernhard A1 - Deng, Y. Y. T1 - Formation of a double-decker magnetic flux rope in the sigmoidal solar active region 11520 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - In this paper, we address the formation of a magnetic flux rope (MFR) that erupted on 2012 July 12 and caused a strong geomagnetic storm event on July 15. Through analyzing the long-term evolution of the associated active region observed by the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, it is found that the twisted field of an MFR, indicated by a continuous S-shaped sigmoid, is built up from two groups of sheared arcades near the main polarity inversion line a half day before the eruption. The temperature within the twisted field and sheared arcades is higher than that of the ambient volume, suggesting that magnetic reconnection most likely works there. The driver behind the reconnection is attributed to shearing and converging motions at magnetic footpoints with velocities in the range of 0.1-0.6 km s(-1). The rotation of the preceding sunspot also contributes to the MFR buildup. Extrapolated three-dimensional non-linear force-free field structures further reveal the locations of the reconnection to be in a bald-patch region and in a hyperbolic flux tube. About 2 hr before the eruption, indications of a second MFR in the form of an S-shaped hot channel are seen. It lies above the original MFR that continuously exists and includes a filament. The whole structure thus makes up a stable double-decker MFR system for hours prior to the eruption. Eventually, after entering the domain of instability, the high-lying MFR impulsively erupts to generate a fast coronal mass ejection and X-class flare; while the low-lying MFR remains behind and continuously maintains the sigmoidicity of the active region. KW - Sun: corona KW - Sun: coronal mass ejections (CMEs) KW - Sun: filaments, prominences KW - Sun: magnetic fields Y1 - 2014 U6 - https://doi.org/10.1088/0004-637X/789/2/93 SN - 0004-637X SN - 1538-4357 VL - 789 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER -