Normal07.8 磅02falsefalsefalseEN-USZH-CNX-NONEDynamic Evolution of an X-shaped structure above a Trans-equatorial Quadrupole Active Region

Time：May4, 2014，Sunday, 10: 00-11:00

Normal07.8 磅02falsefalsefalseEN-USZH-CNX-NONEIn the solar corona, magnetic reconnection usually takes place at the singular configuration of magnetic field, in particular near a magnetic null owing to its high susceptibility to perturbations. In this paper, we report a rare X-shaped structure, encompassing a magnetic null, above a trans- equatorial quadrupole active region that is well observed by the Atmospheric Imaging Assembly (AIA). The observations show that this X-shaped structure is visible in all AIA EUV passbands and stably exists for days. However, possibly induced by flare activities at the northern part of the quadrupole active region, the X-shaped structure starts to destabilize and then causes a jet eruption near its center at∼15:05 UT on 2013 October 7. Through the non-linear force- free field modeling, we identify a magnetic null, which consists of quadrupole polarities and well corresponds to the X-shaped structure. After the jet eruption, the differential emission measure analysis shows that the temperature and emission measure of the plasma near the X-shaped structure rise from∼2.3 MK and∼1.2×1027 cm^−5 at 15:01 UT to∼5.4 MK and∼3.7×1027 cm^−5 at 15:36 UT, respectively, indicating that magnetic reconnection most likely takes place there to heat the plasma and drive the jet eruption. Moreover, the height of the null has an increase of∼10 Mm, which is most likely due to the partial opening of the field lines near the fan surface that makes the null underneath rise to seek for a new equilibrium.

Normal07.8 磅02falsefalsefalseEN-USZH-CNX-NONE

Formation of a Double-Decker Magnetic Flux Rope in the Sigmoidal Solar Active Region 11520

Time：May5, 2014， Monday, 16: 30-17:00

Normal07.8 磅02falsefalsefalseEN-USZH-CNX-NONEWe 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 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 two hours before the eruption, indications for 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.

Normal07.8 磅02falsefalsefalseEN-USZH-CNX-NONE程鑫 男，1985年生于陕西咸阳，2012年获南京大学天文学博士学位。现为南京大学天文与空间科学学院助理研究员。2010年9月至2011年12月在美国乔治梅森大学联合培养。截止目前为止发表SCI论文16篇，其中在国际一流期刊ApJ（Letters）上发表第一作者论文10篇，在国际知名综合性期刊Nature Communications发表第二作者论文1篇，所有论文被引用200多次，国际会议邀请报告2次。2010年获得首届教育部学术新人奖，2011年获美国太阳物理年会学生奖，2012年获南京大学研究生优秀毕业生称号。2013年获得南京大学、江苏省优秀博士论文奖；第七届全国空间天气大会，第三届世界华人空间天气大会优秀论文奖。因为在日冕物质抛射和磁绳探测及演化方面的工作，被美国地球物理大会（AGU）授予2013年度日地系统科学青年科学家Basu奖。