TY - JOUR A1 - Wang, Yi-Ming A1 - Muglach, Karin A1 - Kliem, Bernhard T1 - Endpoint brightenings in erupting filaments N2 - Two well known phenomena associated with erupting filaments are the transient coronal holes that form on each side of the filament channel and the bright post-event arcade with its expanding double row of footpoints. Here we focus on a frequently overlooked signature of filament eruptions: the spike- or fan-shaped brightenings that appear to mark the far endpoints of the filament. From a sample of non-active-region filament events observed with the Extreme- Ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory, we find that these brightenings usually occur near the outer edges of the transient holes, in contrast to the post-event arcades, which define their inner edges. The endpoints are often multiple and are rooted in and around strong network flux well outside the filament channel, a result that is consistent with the axial field of the filament being much stronger than the photospheric field inside the channel. The extreme ultraviolet brightenings, which are most intense at the time of maximum outward acceleration of the filament, can be used to determine unambiguously the direction of the axial field component from longitudinal magnetograms. Their location near the outer boundary of the transient holes suggests that we are observing the footprints of the current sheet formed at the leading edge of the erupting filament, as distinct from the vertical current sheet behind the filament which is the source of the post-event arcade. Y1 - 2009 UR - http://iopscience.iop.org/0004-637X/ U6 - https://doi.org/10.1088/0004-637x/699/1/133 SN - 0004-637X 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 -