A circuit model for filament eruptions and two-ribbon flares
A circuit model for filament eruptions and two-ribbon flares
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DOI：
10.1007/bf00912996
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发表时间：
1989
期刊：
影响因子：
2.8
通讯作者：
P. Martens;N. Kuin
中科院分区：
文献类型：
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作者：
P. Martens;N. Kuin
我们推导了一个太阳暗条爆发和双带耀斑的电路模型，该模型再现了暗条缓慢的能量积累和爆发，以及双带耀斑期间耀斑后环顶部电流片中的能量耗散。在我们的模型中，自由磁能集中在通过灯丝的电流中，另一个电流通过下面的电流片，以及表面返回电流。由这些电流和一个普通光球背景场产生的磁场位形，其拓扑结构类似于观测得到的场拓扑结构。我们考虑两个回路，即灯丝和它的返回电流回路，以及电流片和它的返回电流回路。这些电路是感应耦合和自由能存储在灯丝在预耀斑阶段被发现转移到片在脉冲阶段，并迅速消散。相当数量的磁能被转换成喷出的细丝的动能。该模型的基本方程是细丝和电流片的动量方程，以及细丝和电流片电路的感应方程。方程的推导是Kuperus和Raadu、货车Tend和Kuperus、Syrovatskii和Kaastra先前模型的扩展。方程组是封闭的，在这个意义上说，只有初始条件和一些参数，所有相关的前耀斑观测，需要计算系统的演变。为了确定这些参数，我们需要在耀斑爆发前进行观测：（1）磁象图，（2）α图象，（3）日冕密度的测量，（4）光球速度场的估计。在对暗条电流片系统演化的解中，我们区分出4个阶段：（1）缓慢的能量积累，持续近两天，在此期间，暗条准静态地发展，（2）“亚稳态”状态，持续约三小时，在此期间，暗条易受耀斑触发，并且在此期间，电流片出现，（3）爆发阶段，（4）耀斑后阶段，暗条加速下降，电流片消失。（1）进入灯丝电路的磁通量必须超过一定的阈值才能发生喷发。低于该阈值，我们找到代表静态细丝的解决方案。（2）耀斑触发器对于喷发来说既不是必要的，也不是充分的，但可以在“亚稳”状态期间引发喷发。(3)该模型再现了增加剪切的灯丝喷发前，通过adclineof灯丝电流，在大多数模型相反的灯丝喷发。(4)作为喷出物的动能损失的能量与在耀斑后环中辐射出去的能量的比率敏感地取决于电流片的电阻。(5)耀斑预测是可能的，这个模型，但触发的“亚稳态”状态期间的潜力复杂的预测喷发的确切时刻。
We derive a circuit model for solar filament eruptions and two-ribbon flares which reproduces the slow energy build up and eruption of the filament, and the energy dissipation in a current sheet at the top of post-flare loops during the two-ribbon flare. In our model the free magnetic energy is concentrated in a current through the filament, another current through an underlying current sheet, and surface return currents. The magnetic field configuration, generated by these currents and a general photospheric background field, has a topology similar to the field topology derived from observations.We consider two circuits, that of the filament and its return current, and that of the current sheet and its return current. These circuits are inductively coupled and free energy stored in the filament in the pre-flare phase is found to be transferred to the sheet during the impulsive phase, and rapidly dissipated there. A comparable amount of magnetic energy is converted into kinetic energy of the ejected filament. The basic equations of the model are the momentum equations for the filament and the current sheet, and the induction equations for the filament and sheet circuits. The derivation of the equations is an extension of previous models by Kuperus and Raadu, Van Tend and Kuperus, Syrovatskii, and Kaastra. The set of equations is closed in the sense that only the initial conditions and a number of parameters, all related to pre-flare observables, are needed to calculate the evolution of the system. The pre-flare observations we need to determine these parameters, are: (1) a magnetogram, (2) an α picture, (3) a measurement of the coronal density in the region, and (4) estimates of the photospheric velocity fields in the region.In the solutions for the evolution of the filament current sheet system we distinghuish 4 phases: (1) a slow energy build up, lasting for almost two days, during which the filament evolves quasi-statically, (2) a ‘metastable’ state, lasting for about three hours, during which the filament is susceptible to flare triggers, and during which a current sheet emerges, (3) the eruptive phase, with strong acceleration of the filament, during which a large current is induced and dissipated in the current sheet, and energy is injected in the post-flare loops, and finally (4) a post-flare phase, in which the filament acceleration declines and the current sheet vanishes.From further numerical work we derive the following conclusions: (1) The magnetic flux input into the filament circuit has to surpass a certain threshold for an eruption to occur. Below that threshold we find solutions representing quiescent filaments. (2)Flare triggers are neither necessary nor sufficient for an eruption, but may set off the eruption during the ‘metastable’ state. (3) The model reproduces the increase in shear in the filament prior to the eruption, through adeclineof the filament current, in contrast to most models for filament eruptions. (4) The ratio of energy lost as kinetic energy of ejecta to the energy radiated away in the post-flare loops is sensitively dependent on the resistance of the current sheet. (5) Flare prediction is possible with this model, but the potential for triggering during the ‘metastable’ state complicates the prediction of the exact moment of eruption.