GEM: The Dynamics of a Substorm: Auroral Streamers, Plasmasheet Flows, and Substorm Onset

该项目将调查极光流光与磁尾事件之间的假设联系，磁尾事件导致称为亚暴的大规模极光和地磁扰动。 亚暴是由储存在伸展的磁尾磁场中的能量爆炸性释放提供动力的，但能量释放机制和相关动力学的细节迄今尚未得到解决。了解极光亚暴的成因是空间天气研究中的一个关键问题。 极光流光是该项目的重点，是极光发射中的指状结构，在夜面沿南北方向排列，从极光椭圆的极向边缘向低纬度行进。 对一些事件的观测表明，极光流光是远在磁尾的等离子体爆发流的电离层中的特征。 它们的运动方向表明，爆发流正在从磁尾更远处向地球输送能量和等离子体。 一些研究已经观测到极光流在亚暴爆发之前到达亚暴的初始位置，这导致人们猜测这些气流可能参与了亚暴的触发。如果这是真的，极光流光的特征和运动将很可能为长期争论的亚暴动力学提供新的见解。了解这些大规模的极光和地磁扰动是如何产生的，是有实际原因的。它们导致卫星阻力增加，干扰导航和通信系统，在极端情况下，还可能破坏电网。 这个项目有几个独特的方面。 为了尽量减少或消除观测者的偏差，将采用自动跟踪程序，在孤立的亚暴期间查明所有天空图像中的极光流光。 一种称为点过程统计的技术将用于确定极光流光和亚暴爆发之间是否存在关系。 此外，还将进行相关分析，以研究磁尾爆发流与极光特征之间的关系。 另一个目标是调查亚暴爆发期间极光珠是否始终存在。 极光珠被认为是由磁尾的不稳定性膨胀产生的结构。 一个积极的结果将意味着气球不稳定性有可能在亚暴爆发的作用。

This project will investigate the hypothesized link between auroral streamers and events in the magnetotail leading to large auroral and geomagnetic disturbances called substorms. Substorms are powered by the explosive release of energy stored in the stretched magnetotail fields but the details of the energy release mechanism and associated dynamics have so far not been resolved. Understanding the cause of auroral substorms is a key problem in space weather research. Auroral streamers, the focus of this project, are finger-like structures in the auroral emissions aligned in the north-south direction on the nightside that travel from the poleward edge of the auroral oval towards lower latitudes. Observations for a number of events indicate that the auroral streamers are signature in the ionosphere of bursty flows of plasma far out in the magnetotail. The direction of their motion indicates that the bursty flows are transporting energy and plasma towards Earth from farther out in the magnetotail. A number of studies have observed auroral streamers reaching the initial location of substorms just prior to their explosive onsets leading to speculation that these flows may be involved in substorm triggering. If true, the characteristics and motion of auroral streamers will very likely give fresh insights into the long-debated dynamics of substorms. There are practical reasons for understanding how these large-scale auroral and geomagnetic disturbances are created. They lead to increased satellite drag, interfere with navigation and communications systems, and, in extreme cases, can disrupt electric power grids. This project has several unique aspects. In an effort to minimize or remove observer bias, automatic tracking routines will be applied to identify auroral streamers in all sky images during isolated substorms. A technique called Statistics of Point Processes will be used to determine if there is a relationship between auroral streamers and substorm onsets. In addition, correlation analysis will be performed to investigate the relationship between bursty flows in the magnetotail and auroral features. A further objective will be to investigate whether auroral beads are consistently present during substorm onsets. Auroral beads are structures thought to be produced by the ballooning instability in the magnetotail. A positive result would imply that the ballooning instability has a possible role in substorm onsets.