重复积累电流诱发的日冕急流
Recurrent Coronal Jets Induced by Repetitively Accumulated Electric Currents
摘要：
2010年9月17日，三个极紫外（EUV）喷流在活动区11106的以下磁极在大约一个小时内重现。太阳动力学天文台（SDO）上的大气成像组件（AIA）观测到了EUV喷流。SDO上的日震和磁成像仪（HMI）测量了矢量磁场，从中我们得到了磁通量的演变，光球速度场，和垂直电流的演变。通过非线性无力场（NLFFF）外推，得到了喷流前的磁位形。我们推导出喷流是在一对寄生磁偶极子的上方，这对寄生磁偶极子是由光球发散流连续驱动的。这种相互作用推动了电流的积累，我们确实在光球层上观察到了拉长的图案。这是第一次，HMI的高时间节奏允许跟踪这种小电流的演变。在喷流区，我们发现积分绝对电流峰与171 A通量演化重复同相。电流的建立和衰减都很快，大约各10分钟，并且电流最大值也比171 A提前大约10分钟。然后，HMI时间节奏足够快以检测这种变化。光球电流图案的喷流被发现与准分界线层推导出的磁外推。从以前的理论结果，观察到的发散流预计将建立连续这样的电流。我们的结论是，磁重联周期性地发生，在新兴的双极和大尺度活动区场之间的电流层。它导致了观测到的经常性日冕喷流和垂直电流大小的减小。
英文摘要：
Three extreme-ultraviolet (EUV) jets recurred in about one hour on 2010 September 17 in the following magnetic polarity of active region 11106. The EUV jets were observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The Helioseismic and Magnetic Imager (HMI) on board SDO measured the vector magnetic field, from which we derive the magnetic flux evolution, the photospheric velocity field, and the vertical electric current evolution. The magnetic configuration before the jets is derived by the nonlinear force-free field (NLFFF) extrapolation. We derive that the jets are above a pair of parasitic magnetic bipoles which are continuously driven by photospheric diverging flows. The interaction drove the build up of electric currents that we indeed observed as elongated patterns at the photospheric level. For the first time, the high temporal cadence of HMI allows to follow the evolution of such small currents. In the jet region, we found that the integrated absolute current peaks repetitively in phase with the 171 A flux evolution. The current build up and its decay are both fast, about 10 minutes each, and the current maximum precedes the 171 A by also about 10 minutes. Then, HMI temporal cadence is marginally fast enough to detect such changes. The photospheric current pattern of the jets is found associated to the quasi-separatrix layers deduced from the magnetic extrapolation. From previous theoretical results, the observed diverging flows are expected to build continuously such currents. We conclude that magnetic reconnection occurs periodically, in the current layer created between the emerging bipoles and the large scale active region field. It induced the observed recurrent coronal jets and the decrease of the vertical electric current magnitude.
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