极盖区极光弧的形成机制和演化特征研究

Polar cap arcs (PCAs) are defined as high-latitude auroral arcs in the polar cap region. Some arcs extend from the nightside to the dayside across the central polar cap and connect the dayside and nightside auroral oval. Some arcs are relatively shorter in length and tend to occur either on the duskside or dawnside of the polar cap. Other arcs are only connected to one side of the main auroal oval or even completely detached from the auroral oval and move into the polar cap. It is very helpful to study the behavior of the polar cap arcs for a comprehensive understanding of the solar wind-magnetosphere-ionosphere coupling processes. To data, however, there have been some controversies in the studies of polar cap arcs. On the one hand, whether polar cap arc occur on closed or open field lines is inconclusive; on the other hand, conjugacy issue or (a)symmetric auroral characteristics between the northern and southern hemispheres is not clear. We investigate the formation and evolution features of the polar cap arcs with case analysis and statistical studies, to study dynamical characteristics of their source plasma in the magnetosphere and the symmetric or asymmetric auroral features in both hemispheres and to discuss the formation and evolution physical mechanisms, based on a large number of PCA cases we detected by the ground-based all-sky imagers at the Chinese Yellow River Station, Zhong Shan Station and Resolute Bay, Canada, together with the observations from the space-based imagers of IMAGE/POLAR/TIMED, the EISCAT/SuperDARN radar, and the THEMIS/Cluster/MMS/DMSP/SWARM satellites.

极盖区极光弧是指发生在极盖区内的弧状极光结构，有些从夜侧向日侧延伸可跨越整个极盖区并连接日、夜侧极光卵，有些仅位于极盖区晨侧或昏侧且尺度较短，还有一些只与极光卵一头相连或完全脱离极光卵进入极盖区。极盖区极光弧的研究对深入理解太阳风-磁层-电离层耦合过程具有重要意义。目前，对极盖区极光弧的研究尚存争议，一方面其磁力线位型是否为闭合尚无定论；另一方面，其南北半球对比特性也不明确。针对上述问题，本项目拟在利用我国北极黄河站和南极中山站以及加拿大Resolute Bay的全天空极光观测已检出的大量极盖区极光弧事件基础上，联合IMAGE/POLAR/TIMED星载极光成像观测、地基雷达和THEMIS/Cluster/MMS/DMSP/SWARM卫星等的协同观测，采用事件分析和统计研究相结合的方法，深入分析各类极盖区极光弧的沉降粒子源区特性及南北半球对比特性，探讨其产生和演化的物理机制。

极盖区极光弧是指发生在极盖区内的弧状极光结构，它常常发生在地磁平静且行星际磁场北向期间，是太阳风-磁层-电离层耦合过程在极区电离层的典型踪迹之一。然而，目前对极盖区极光弧的研究存在争议，尤其是其磁力线位型是否闭合以及南北半球对比特性尚无定论。本项目我们主要利用地基和星载极光观测数据，联合雷达、卫星等多手段观测，研究了极盖区极光弧的沉降粒子特征、南北半球对比特性，探讨其磁力线位型及产生和演化的物理机制以及相关物理过程的空间天气学效应等。重要结果如下：发现在南北半球同时观测到的极盖区极光弧的运动明显受行星际磁场By的调制，而且在南北半球呈现出明显的反对称特征，在极盖区内已形成的极光弧的运动明显受行星际磁场By调制；极盖区极光弧伴随有很强的对流剪切/反转，其沉降粒子具有边界层等离子体的特征；我们推测该极盖区极光弧发生在闭合磁力线上。极盖区极光弧的粒子沉降能引起一种与传统极盖区等离子体云块不同的热等离子体云块，其电子温度明显升高，并伴随有离子上行、场向电流和对流剪切，能引起更强的极区电离层闪烁；统计发现离子/电子温度比等于0.8是区分传统和热等离子体云块的界线。首次观测证实了两种标准闪烁指数与极区电离层对流速度存在很好的相关性，相位闪烁比幅度闪烁随对流速度增加地更快。这些研究工作有助于深入理解太阳风-磁层-电离层耦合过程，深入理解极盖区内不均匀体的形成和演化物理机理及其空间天气学效应，为极区电离层建模和空间天气预报提供物理依据。