2011年8月4日螺旋状日冕物质抛射爆发事件

利用多卫星多波段的综合观测数据，通过追踪光球表面等离子体速度分析计算了耀斑爆发前后磁螺度的变化，发现耀斑爆发前活动区中光球表面存在强的水平剪切运动，活动区磁螺度的注入主要由这种剪切运动所产生；使用CESE-MHD-NLFFF重建了耀斑爆发前后活动区的磁场位形，推测出耀斑过程中存在磁绳结构的抛射.基于这些分析，给出了这一螺旋状抛射结构的形成机制:爆发前暗条西侧足点的持续剪切运动驱动磁通量绳增加扭转，高度扭缠的通量绳与东侧足点附近的开放磁力线重联并与东侧足点断开，进而向外抛出并伴随解螺旋运动.另外，利用1AU处WIND卫星的观测数据在对应的行星际日冕物质抛射中找到典型磁云的观测特征.这表明除了传统上双足点均在太阳表面的磁云模型，这种单足点固定于太阳表面的磁通量绳爆发图景同样可能在行星系际空间形成磁云结构.研究结果对进一步认识磁云结构具有重要意义. 

Twisted Coronal Mass Ejection on 4 August 2011

On 4 August 2011, a GOES M9.3 flare with a fast coronal mass ejection was erupted from solar active region NOAA AR11261. After the flare, a rotating structure is observed by STEREO, in which the rotating motion lasted about 4 hours. The magnetic helicity flux associated with the flare was calculated based on the SDO/HMI vector magnetograms by tracking the plasma velocity of the photosphere. It is found that the photospheric shear and twist motion contribute significantly to the magnetic helicity injection before the flare. The coronal magnetic fields were extrapolated using the CESE-MHD-NLFFF code, which shows that twisted magnetic flux rope exists before the flare and disappears after the flare. With these analyses, a scenario for the formation and evolution of this eruption is suggested as follows. The rotation of the foot point on the west side of the eruption filament twisted the magnetic flux rope, and the highly twisted structure became unstable and erupted. During the eruption, it reconnected with open magnetic field lines near one leg, and a long duration of untwisting movement followed the eruption. Interestingly, the observations of WIND satellites at 1AU show characteristics of typical magnetic clouds in the corresponding interplanetary coronal mass ejections of this eruption, which indicates that a magnetic cloud might be a flux rope with one leg anchored on the Sun, and it is not previously considered.