Interaction between Multiple Current Sheets and a Shock Wave: 2D Hybrid Kinetic Simulations
Interaction between Multiple Current Sheets and a Shock Wave: 2D Hybrid Kinetic Simulations
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DOI：
10.3847/1538-4357/ac2e06
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发表时间：
2021-12
期刊：
影响因子：
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通讯作者：
M. Nakanotani;G. Zank;L.-L. Zhao-L.
中科院分区：
文献类型：
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作者：
M. Nakanotani;G. Zank;L.-L. Zhao-L.
近年来，由于日球层中磁岛之间的相互作用而引起的冲击波后面的粒子加速引起了人们的关注。下游加速可以产生冲击波下游的颗粒通量的连续增加。虽然下游磁岛是如何产生的还不清楚，但有人认为，由于磁岛与冲击波的相互作用，电流片参与了磁岛的产生。我们进行二维混合动力学模拟，研究多个电流片和冲击波之间的相互作用。在模拟中，电流片被压缩的冲击波和撕裂不稳定性的发展在压缩的电流片下游的冲击。由于这种不稳定性，电磁场变得湍流，并且在冲击波的下游形成磁岛。我们发现了一个“后标”区域，在该区域中，垂直于下游静止坐标系中的激波的下游流速在激波后面立即减速到101 VA，其中VA是上游Alfvén速度。然后，随着撕裂不稳定性的发展，流动速度逐渐减速到0。我们还观察到一个有效的生产高能粒子100 E 0以上的冲击波，其中E0= mpVA 2和MP是质子质量的不稳定性的发展过程中的一些距离下游。这一特征与旅行者号的观测结果相对应，旅行者号的观测结果表明，宇宙射线强度的异常增加开始于日光层终止激波下游的某个距离处。
Particle acceleration behind a shock wave due to interactions between magnetic islands in the heliosphere has attracted attention in recent years. The downstream acceleration may yield a continuous increase of particle flux downstream of the shock wave. Although it is not obvious how the downstream magnetic islands are produced, it has been suggested that current sheets are involved in the generation of magnetic islands due to their interaction with a shock wave. We perform 2D hybrid kinetic simulations to investigate the interaction between multiple current sheets and a shock wave. In the simulation, current sheets are compressed by the shock wave and a tearing instability develops at the compressed current sheets downstream of the shock. As the result of this instability, the electromagnetic fields become turbulent and magnetic islands form well downstream of the shock wave. We find a “post-cursor” region in which the downstream flow speed normal to the shock wave in the downstream rest frame is decelerated to ∼ 1V A immediately behind the shock wave, where V A is the upstream Alfvén speed. The flow speed then gradually decelerates to 0 accompanied by the development of the tearing instability. We also observe an efficient production of energetic particles above 100 E 0 during the development of the instability some distance downstream of the shock wave, where E0=mpVA2 and m p is the proton mass. This feature corresponds to Voyager observations showing that the anomalous cosmic-ray intensity increase begins some distance downstream of the heliospheric termination shock.