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  - 
TY  - JOUR
A1  - Tilmann, F.
A1  - Zhang, Y.
A1  - Moreno, M.
A1  - Saul, J.
A1  - Eckelmann, F.
A1  - Palo, M.
A1  - Deng, Z.
A1  - Babeyko, Andrey
A1  - Chen, K.
A1  - Báez, Juan Carlos
A1  - Schurr, B.
A1  - Wang, R.
A1  - Dahm, Torsten
T1  - The 2015 Illapel earthquake, central Chile: A type case for a characteristic earthquake?
JF  - Geophysical research letters
N2  - On 16 September 2015, the M-W = 8.2 Illapel megathrust earthquake ruptured the Central Chilean margin. Combining inversions of displacement measurements and seismic waveforms with high frequency (HF) teleseismic backprojection, we derive a comprehensive description of the rupture, which also predicts deep ocean tsunami wave heights. We further determine moment tensors and obtain accurate depth estimates for the aftershock sequence. The earthquake nucleated near the coast but then propagated to the north and updip, attaining a peak slip of 5-6 m. In contrast, HF seismic radiation is mostly emitted downdip of the region of intense slip and arrests earlier than the long period rupture, indicating smooth slip along the shallow plate interface in the final phase. A superficially similar earthquake in 1943 with a similar aftershock zone had a much shorter source time function, which matches the duration of HF seismic radiation in the recent event, indicating that the 1943 event lacked the shallow slip.
Y1  - 2016
U6  - https://doi.org/10.1002/2015GL066963
SN  - 0094-8276
SN  - 1944-8007
VL  - 43
SP  - 574
EP  - 583
PB  - American Geophysical Union
CY  - Washington
ER  -