P. Levens, A. Norton, M. Linton, K. Knizhnik, Y. Liu
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引用次数: 0
摘要
我们在三个δ (δ)-太阳黑子的孤立磁节中测量了电流的螺旋度(H r c)以及扭曲(α r)和扭曲(W)的代用物,并报告了观测结果与高扭曲磁管上的扭结不稳定性相一致。δ斑是正负影共用半影的活动区域。我们识别并分离了“磁结”,即在ARs NOAA 11158, 11267和11476中,用太阳动力观测站日震和磁成像仪的数据观测到的相反极性的薄膜,它们靠近并形成了δ配置。我们发现H r c, α r和W对于每个磁结具有相同的符号,正如在高扭流管上的扭结不稳定性模拟中所预测的那样。引起δ-形成的变形磁通管,即磁结,只是整个磁通圈的一部分,并表明了磁通圈不稳定性在更小的空间尺度上发挥作用的可能性。每个磁脚点包含一个径向电流的符号,J r,这表明我们正在观察没有回流电流的磁通圈的核心。作为一个反例,我们分析了一个β点,表明H r c和α r具有与w相反的符号。虽然我们的观察支持δ点中磁结的形成机制是扭结不稳定性,但需要更大的样本来确定扭结不稳定性是磁管变形的原因。
Observations of Twist, Current Helicity, and Writhe in the Magnetic Knots of δ-sunspots Consistent with the Kink Instability of a Highly Twisted Flux Rope
We measure current helicity (H r c ) as well as proxies for twist (α r ) and writhe (W) in the isolated magnetic knots of three delta (δ)-sunspots and report that the observations are consistent with a kink instability acting on a highly twisted flux tube. δ-spots are active regions (ARs) in which positive and negative umbrae share a penumbra. We identify and isolate “magnetic knots,” i.e., opposite polarity umbrae that are in close proximity and forming the δ-configuration, in ARs NOAA 11158, 11267, and 11476 as observed with data from the Solar Dynamic Observatory Helioseismic and Magnetic Imager. We find that H r c , α r , and W have the same sign for each magnetic knot, as predicted in simulations of a kink instability acting on highly twisted flux tubes. The deformed flux tube causing the δ-formation, the magnetic knot, is only a portion of the entire AR and demonstrates the potential for the kink instability to act on a smaller spatial scale within the AR. Each magnetic footpoint contains a single sign of the radial current, J r , which suggests that we are observing the core of the flux rope without return currents. As a counterexample, we analyze one β-spot that shows H r c and α r have the opposite signs of W. While our observations support the formation mechanism of the magnetic knots in δ-spots being the kink instability, a much larger sample is needed to determine confidently the prevalence of the kink instability as the cause of flux tube deformation.