标题： 耀斑前太阳日冕磁场的研究：磁通绳 显示英文标题

标题： A Study of Pre-Flare Solar Coronal Magnetic Fields: Magnetic Flux Ropes

摘要： 磁通量绳（MFRs）被认为是太阳爆发的中心结构，其理想化的MHD不稳定性可以触发爆发。 在这里，我们研究了从2011年到2017年太阳盘面中心附近的导致主要太阳耀斑的所有MFR构型，这些耀斑可能是爆发性的也可能是限制性的。 日冕磁场通过观测的磁图重建，基于磁扭曲分布，我们识别出MFR，定义为一组相干的磁力线绕轴缠绕超过一圈。 发现90%的事件具有前耀斑MFR，它们的三维结构比理论MFR模型更为复杂。 我们进一步基于控制扭结不稳定的磁扭曲数和控制气球不稳定的衰减指数这两个参数构建了一个图。 它清楚地显示了TI和KI阈值的下限，分别为$n_{\rm crit} = 1.3$和$|T_w|_{\rm crit} = 2$，因为所有超过$n_{\rm crit}$的事件以及近90%的超过$|T_w|_{\rm crit}$的事件都爆发了。 此外，根据这一标准，超过70%的事件可以区分爆发性和限制性耀斑，扭结不稳定性似乎与气球不稳定性在区分这两种耀斑方面起着几乎同样重要的作用。 有超过一半的事件两个参数都在下限以下，其中29%是爆发性的。 这些事件可能由磁重联触发而不是由MHD不稳定性触发。 显示英文摘要

摘要： Magnetic flux ropes (MFRs) are thought to be the central structure of solar eruptions, and their ideal MHD instabilities can trigger the eruption. Here we performed a study of all the MFR configurations that lead to major solar flares, either eruptive or confined, from 2011 to 2017 near the solar disk center. The coronal magnetic field is reconstructed from observed magnetograms, and based on magnetic twist distribution, we identified the MFR, which is defined as a coherent group of magnetic field lines winding an axis with more than one turn. It is found that 90% of the events possess pre-flare MFRs, and their three-dimensional structures are much more complex in details than theoretical MFR models. We further constructed a diagram based on two parameters, the magnetic twist number which controls the kink instability (KI), and the decay index which controls the torus instability (TI). It clearly shows lower limits for TI and KI thresholds, which are $n_{\rm crit} = 1.3$ and $|T_w|_{\rm crit} = 2$, respectively, as all the events above $n_{\rm crit}$ and nearly 90% of the events above $|T_w|_{\rm crit}$ erupted. Furthermore, by such criterion, over 70% of the events can be discriminated between eruptive and confined flares, and KI seems to play a nearly equally important role as TI in discriminating between the two types of flare. There are more than half of events with both parameters below the lower limits, and 29% are eruptive. These events might be triggered by magnetic reconnection rather than MHD instabilities.