Collaborative Research: Super-Alfvenic propagation of energy released during magnetic reconnection in the Earth's magnetotail

磁重联在磁尾动力学中起着至关重要的作用，通过重新配置磁拓扑来释放存储的磁能。从重联点传播的能量的性质对我们理解瞬态磁尾现象，如突发体流、双极化锋和亚暴具有重要意义。虽然宇宙飞船直接测量了因重联而加速的大量离子流动，并将其与极光的产生联系起来，但这种能量的传播速度仅限于阿尔夫萨芬速度，而且有证据表明，能量的传播速度必须快于阿尔夫萨芬速度，才能解释亚暴的发生。然而，不太清楚的是，与动态电子动力学相关的超阿尔夫萨奇能量流往往发生在磁分离层附近。与霍尔动力学相关的这一区域的四极磁场已被证明是动态阿尔夫萨芬波（KAW）的表现，该波与磁场平行传播超阿尔夫萨芬波，并产生与高能电子流相关的大量坡因廷通量。本研究将研究控制重联能量超光速传播的基本物理机制，主要集中在中尾区域。该研究将使用动能粒子单元模拟（PIC）和来自星团和THEMIS航天器的重联卫星观测。这应该是理解重联开始和瞬态磁尾现象（如突发体流、双极化锋和亚暴开始）之间因果关系的重要一步。然而，这项研究的潜在好处超出了磁尾研究，因为重联能量的传播是一个重要的问题，对于广泛的天然等离子体和实验室等离子体。

Magnetic reconnection plays a fundamental role in magnetotail dynamics, reconfiguring magnetic topology to release stored magnetic energy. The nature of the energy propagating away from the reconnection site has implications for our understanding of transient magnetotail phenomena such as bursty bulk flows, dipolarization fronts and substorms. While bulk ion flows accelerated by reconnection have been measured directly by spacecraft and have been linked to the generation of aurora the propagation speed of this energy is limited to the Alfvén speed and there is evidence that energy must propagate faster than the Alfvén speed to account for substorm onset. Less well understood, however, are super-Alfvénic flows of energy associated with kinetic electron dynamics which tend to occur near the magnetic separatrices. The quadrupolar magnetic fields in this region associated with Hall dynamics have been shown to be the manifestation of a kinetic Alfvén wave (KAW) that propagates super-Alfvénically parallel to the magnetic field and generates substantial Poynting flux associated with energetic electron streams. This investigation will study the basic physics mechanisms controlling the super-Alfvénic propagation of reconnection energy with focus roughly on the mid-tail region. The study will use kinetic particle-in-cell simulations (PIC) and satellite observations of reconnection from the Cluster and THEMIS spacecraft. This should be a significant step towards understanding the causal relationships between reconnection onset and transient magnetotail phenomena such as bursty bulk flows, dipolarization fronts, and substorm onset. However the potential benefit of this research extends beyond magnetotail research because propagation of reconnection energy is an important problem for a wide range of natural plasmas and laboratory plasmas.