NUMERICAL SIMULATIONS OF HELICITY CONDENSATION IN THE SOLAR CORONA
NUMERICAL SIMULATIONS OF HELICITY CONDENSATION IN THE SOLAR CORONA
复制标题
日冕螺旋凝聚的数值模拟
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
T. Zurbuchen
中科院分区：
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作者：
L. Zhao;C. DeVore;S. Antiochos;T. Zurbuchen
安提奥科斯提出了螺旋度凝聚模型来解释观测到的日冕环的平滑性和观测到的磁剪切在暗条通道的积累。该模型的基本假设是，日冕中的磁场重联导致光球运动注入的磁应力仅在观察到双折射形成的那些特殊位置处聚集。在这项工作中，我们提出了第一个详细的定量MHD模拟的螺旋度凝聚模型提出的重联演变。我们使用众所周知的模拟封闭的日冕作为一个最初的两个水平光球板之间的均匀场的Anastasia。该系统是通过应用光球旋转流注入磁螺旋到日冕驱动。这些流动被限制在光球上的有限区域内，以模拟例如双极活动区域的有限通量系统。计算表明，与通常的看法相反，相反的螺旋度扭曲不会导致在这样的日冕系统显着的重联，而具有相同螺旋度的扭曲确实产生实质性的重联。此外，我们发现，对于一个给定量的注入到日冕的螺旋度，磁剪切的演变是不敏感的驱动光球运动的模式是固定的或准随机的。在所有情况下，剪切传播通过重联的边界的流动区域，而总的磁螺旋度是保守的，如模型所预测的。我们讨论了我们的结果对太阳观测和未来的影响，更现实的螺旋度凝结过程的模拟。
The helicity condensation model has been proposed by Antiochos to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences are observed to form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the corona. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of a bipolar active region, for example. The calculations demonstrate that, contrary to common belief, opposite helicity twists do not lead to significant reconnection in such a coronal system, whereas twists with the same sense of helicity do produce substantial reconnection. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.