Comparison of magnetic energy and helicity in coronal jet simulations
Comparison of magnetic energy and helicity in coronal jet simulations
复制标题
日冕喷流模拟中磁能和螺旋度的比较
DOI：
10.1051/0004-6361/202245142
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发表时间：
2023
影响因子：
6.5
通讯作者：
Pariat E
中科院分区：
文献类型：
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作者：
Pariat E
背景虽然非势能(自由)磁能是日冕中任何活跃现象的必要元素，但它作为触发喷发过程的标志的作用仍然难以捉摸。同时，最近对太阳活动事件数值模拟的分析表明，基于相对磁螺旋度的量可以突出太阳磁系统的喷发性质。目的基于磁场被唯一地分解为势分量和非势分量，磁能和螺旋度也都可以唯一地分解为两个量。使用两个可以产生日冕喷流的构型的三维磁流体参数模拟，比较了磁能和相对磁螺旋的动力学。方法两种模拟都具有相同的初始设置和线绑扎的底边界驱动轮廓。然而，它们在强迫的持续时间上是不同的。在一次模拟中，系统被充分驱动，以至于通过一个不返回点，系统诱导产生螺旋喷流。然而，在驱动阶段结束后，喷流的产生明显延迟；在最终诱导喷流之前，会发生一段相对较长的低强度重联阶段。在另一种参考模拟中，系统在较短的时间内被驱动，并且没有产生喷流。结果正如预期的那样，我们观察到产生喷流的模拟包含了比非喷发系统更高的非势能和非势螺旋度。聚焦在驱动阶段结束到喷流产生之间的阶段，我们注意到磁能保持相对恒定，而磁旋度有明显的变化。在后驱动阶段，非位势与总磁能之比略有下降，而螺旋度喷发指数(非位势螺旋度与总相对磁螺旋度之比)显著增大。喷流是在系统处于螺旋度喷发指数的最高值时产生的。在喷气生成阶段，该代理急剧减少。当喷流产生时，自由能也降低，但没有出现任何峰值。结论进一步加强了螺旋度，特别是螺旋度喷发度指数的重要性，以了解太阳喷发事件的触发机制。
ContextWhile non-potential (free) magnetic energy is a necessary element of any active phenomenon in the solar corona, its role as a marker of the trigger of the eruptive process remains elusive. Meanwhile, recent analyses of numerical simulations of solar active events have shown that quantities based on relative magnetic helicity could highlight the eruptive nature of solar magnetic systems.AimsBased on the unique decomposition of the magnetic field into potential and non-potential components, magnetic energy and helicity can also both be uniquely decomposed into two quantities. Using two 3D magnetohydrodynamics parametric simulations of a configuration that can produce coronal jets, we compare the dynamics of the magnetic energies and of the relative magnetic helicities.MethodsBoth simulations share the same initial setup and line-tied bottom-boundary driving profile. However, they differ by the duration of the forcing. In one simulation, the system is driven sufficiently so that a point of no return is passed and the system induces the generation of a helical jet. The generation of the jet is, however, markedly delayed after the end of the driving phase; a relatively long phase of lower-intensity reconnection takes place before the jet is eventually induced. In the other reference simulation, the system is driven during a shorter time, and no jet is produced.ResultsAs expected, we observe that the jet-producing simulation contains a higher value of non-potential energy and non-potential helicity compared to the non-eruptive system. Focussing on the phase between the end of the driving-phase and the jet generation, we note that magnetic energies remain relatively constant, while magnetic helicities have a noticeable evolution. During this post-driving phase, the ratio of the non-potential to total magnetic energy very slightly decreases while the helicity eruptivity index, which is the ratio of the non-potential helicity to the total relative magnetic helicity, significantly increases. The jet is generated when the system is at the highest value of this helicity eruptivity index. This proxy critically decreases during the jet-generation phase. The free energy also decreases but does not present any peak when the jet is being generated.ConclusionsOur study further strengthens the importance of helicities, and in particular of the helicity eruptivity index, to understand the trigger mechanism of solar eruptive events.