Chromospheric magnetic reconnection: two-fluid simulations of coalescing current loops
Chromospheric magnetic reconnection: two-fluid simulations of coalescing current loops
复制标题
色球磁重联：聚结电流环路的双流体模拟
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
J. Sakai
中科院分区：
文献类型：
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作者：
P. Smith;J. Sakai
目标。我们调查磁重联率在合并过程中的两个电流环在太阳色球层，通过改变中性氢质子密度比，电离/重组系数，碰撞频率，和相对螺旋度的循环。方法.我们使用了一个新开发的双流体（离子中性）的数值代码进行2.5D模拟的合并色球电流环。从人工风计划，数字代码包括离子中性碰撞，电离/复合，热/电阻扩散率，碰撞/电阻加热的影响。结果结果发现，磁重联的速率强烈地依赖于中性氢与质子的密度比：密度比增加一千倍，磁重联的速率降低二十倍。这一结果意味着，在离子（质子）和中性氢密度相当的上层色球层中，磁重联的速度明显快于中性氢密度超过离子密度一千倍的下层色球层。这一结果也意味着与快速磁重联相关的喷流倾向于发生在上色球层/下日冕。电离/复合是色球层中的一个重要物理效应，它增加了总的重联磁通量，但不会改变磁重联的速率。离子与中性粒子碰撞频率的降低会导致磁场重联率的小幅增加。两个电流环的相对螺旋度没有观察到对磁重联率有任何显着影响。两种流体和MHD（磁流体动力学）模拟的比较显示显着的差异，特别是对于较高的中性密度的情况下，代表较低的色球层的磁重联率的测量。这说明MHD模型不适合于模拟太阳色球层的磁场重联。结论.磁重联率的合并电流环的强烈影响的中性氢粒子的列入。因此，离子中性碰撞是必不可少的，包括在未来的分析/数值模式的色球磁场重联。
Aims. We investigate magnetic reconnection rates during the coalescence of two current loops in the solar chromosphere, by altering the neutral-hydrogen to proton density ratio, ionisation/recombination coefficients, collision frequency, and relative helicity of the loops. Methods. We used a newly developed two-fluid (ion-neutral) numerical code to perform 2.5D simulations of coalescing chromospheric current loops. Developed from the Artificial Wind scheme, the numerical code includes the effects of ion-neutral collisions, ionisation/recombination, thermal/resistive diffusivity, and collisional/resistive heating. Results. It was found that the rates of magnetic reconnection strongly depend on the neutral-hydrogen to proton density ratio: increasing the density ratio a thousandfold decreased the rate of magnetic reconnection twentyfold. This result implies that magnetic reconnection proceeds significantly faster in the upper chromosphere, where the density of ions (protons) and neutral-hydrogen is comparable, than in the lower chromosphere, where the density of neutral-hydrogen is over a thousand times the ion density. This result also implies that jets associated with fast magnetic reconnection tends to occur in the upper chromosphere / lower corona. The inclusion of ionisation/recombination, an important physical effect in the chromosphere, increases the total reconnected magnetic flux, but does not alter the rate of magnetic reconnection. Reductions in the ion-neutral collision frequency result in small increases to the rates of magnetic reconnection. The relative helicity of the two current loops was not observed to have any significant effect on the rates of magnetic reconnection. Comparisons of two-fluid and MHD (Magnetohydrodynamic) simulations show significant differences in the measured rates of magnetic reconnection, particularly for the higher neutral density cases which represent the lower chromosphere. This demonstrates that MHD is not an appropriate model for simulating magnetic reconnection in the solar chromosphere. Conclusions. The magnetic reconnection rates of coalescing current loops are strongly affected by the inclusion of neutral-hydrogen particles. It is therefore essential that ion-neutral collisions are included in future analytical/numerical models of chromospheric magnetic reconnection.