Successive injection of opposite magnetic helicity in solar active region NOAA 11928
Successive injection of opposite magnetic helicity in solar active region NOAA 11928
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DOI：
10.1051/0004-6361/201629282
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发表时间：
2016-11
影响因子：
6.5
通讯作者：
P. Vemareddy;P. Démoulin
中科院分区：
文献类型：
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作者：
P. Vemareddy;P. Démoulin
目标。理解光球螺旋度通量传输的性质和演化，对于揭示磁螺旋度在太阳活动区日冕动力学中的作用至关重要。方法.我们计算了边界驱动的螺旋度通量与12分钟的节奏，在出现的AR 11928使用SDO/HMI光球矢量磁图和推导出的流速场。考虑到由非线性无力外推定义的足点连通性，我们推导并分析了螺旋度通量图的校正分布。结果光球螺旋度通量注入被发现在AR稳定出现期间改变符号。这一逆转证实了光球电流的演变和日冕的连通性，在EUV波长与SDO/AIA观察。在大约出现的前三天，AR日冕螺旋度是积极的，而后来的字段配置是接近一个潜在的领域。正如理论上预期的那样，磁螺旋度的抵消与日冕活动的增强有关。结论.研究表明，边界驱动的全球AR磁结构的手征性的转变。这可能是由于磁通绳在其顶点周围具有正扭转而在其腿中具有负扭转的结果。这种混合螺旋度通量绳在对流区的起源是具有挑战性的模式。
Aims. Understanding the nature and evolution of the photospheric helicity flux transfer is crucial to revealing the role of magnetic helicity in coronal dynamics of solar active regions. Methods. We computed the boundary-driven helicity flux with a 12-min cadence during the emergence of the AR 11928 using SDO/HMI photospheric vector magnetograms and the derived flow velocity field. Accounting for the footpoint connectivity defined by nonlinear, force-free magnetic extrapolations, we derived and analyzed the corrected distribution of helicity flux maps. Results. The photospheric helicity flux injection is found to change sign during the steady emergence of the AR. This reversal is confirmed with the evolution of the photospheric electric currents and with the coronal connectivity as observed in EUV wavelengths with SDO/AIA. During approximately the three first days of emergence, the AR coronal helicity is positive while later on the field configuration is close to a potential field. As theoretically expected, the magnetic helicity cancellation is associated with enhanced coronal activity. Conclusions. The study suggests a boundary driven transformation of the chirality in the global AR magnetic structure. This may be the result of the emergence of a flux rope with positive twist around its apex while it has negative twist in its legs. The origin of such mixed helicity flux rope in the convective zone is challenging for models.