地球磁尾磁通量绳的产生和演化

Magnetic flux tube is one kind of three-dimensional helical magnetic structures, and it has close relation with explosive phenomena in space plasma, such as the earth's substorm, solar flare and coronal mass ejection. In the earth's magnetotail, the observational charcteristics of magnetic flux tubes are the bipolar structure of Bz and enhancement of By. It is generally accepted that magnetic flux tubes are produced during magnetic reconnection. Because of the close magnetic field lines in flux tubes, plasma is easy to be trapped in flux tubes, and these flux tubes will be compressed during their propagation toward the earth. Therefore, magnetic flux tubes are considered to play an important role in the energy transportation and particle acceleration in the earth's magnatotail. We will use three-dimensional global hybird simulations, combined with local particle-in-cell simulations and satallite observations, to study the production and three-dimensional structures of magnetic flux tubes in the magnetotail, their interactions with each other, their propagation and interactions with the dipole field of the earth. We will also discuss how these flux tubes will affect the energy transport and particle acceleration in the magnetotail, and at last evaluate the roles in substorms.

磁通量管是一种三维螺旋状磁场结构，它和地球磁层亚暴、太阳耀斑和日冕物质抛射等空间等离子体环境中的爆发性事件有着密切的关系。在地球磁尾，磁通量管的观测特征主要表现为Bz的双极结构和By的增强，通常认为是磁重联产生了地球磁尾的磁通量管，同时因其闭合的磁力线位型可相对容易地捕获等离子体，并且这些磁通量管在向地球的传播过程中会发生压缩等形变，因而被认为在地球磁尾的能量传输和带电粒子的加速过程中起着重要的作用。我们拟通过三维的全球混合模拟程序，并结合局地的粒子模拟程序和卫星观测，研究地球磁尾磁通量管的产生、它们的三维结构、磁通量管之间的相互作用、它们在地球磁尾的传播及和地球偶极场的相互作用过程，讨论磁通量管的存在对地球磁尾的能量传输和带电粒子加速过程的影响，最后定量地评估磁通量管在地球磁层亚暴这一爆发性过程中所起的作用。

地球日侧磁层顶和磁鞘中的磁场重联在太阳风中能量传输进入地球磁层的过程中起着重要作用，和磁尾重联不同，这些重联发生的电流片两侧的等离子体参数往往是不同的，发生的是非对称重联。.我们首先用粒子模拟研究了非对称重联中Hall磁场的位型，发现不同于对称重联的四极型分布，非对称重联的Hall磁场可形成四极、五极和六极分布。在无引导场时，Hall磁场先是形成四极分布，后又演化为六极；引导场可导致两侧出流区Hall磁场的非对称分布，一侧为二极，一侧为三极，总体为五极。.我们还用全球的混合模拟研究了磁层顶和磁鞘中的磁场重联。磁层顶处的重联是多X线的，形成的通量管会向南北极移动，有一部分通量管会相互靠近并触发二次重联，有一部分通量管移动到极隙区后触发另外一种二次重联，导致通量管合并到极隙区。激波下游的磁鞘中存在着很强的湍动并可形成电流片，在这些电流片中会发生磁场重联，并形成磁通量管。