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

这个项目将研究极光飘带和磁尾事件之间的假设联系，磁尾导致了被称为亚暴的大极光和地磁扰动。亚暴是由储存在拉伸磁尾场中的能量爆炸释放而产生的，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气象研究中的一个关键问题。极光飘带是这个项目的重点，是指状的结构，在极光发射中沿着南北方向排列在夜晚的一面，从极光椭圆形的极地边缘向低纬度地区传播。对许多事件的观测表明，极光流是电离层中远至磁尾的等离子体爆发流的特征。它们的运动方向表明，爆发流正在将能量和等离子体从更远的磁尾中输送到地球。许多研究已经观察到，在亚暴爆发之前，极光流到达了亚暴的初始位置，这导致人们猜测这些流可能与亚暴的触发有关。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。理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。它们会增加卫星阻力，干扰导航和通信系统，在极端情况下，还会破坏电网。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，自动跟踪程序将应用于在孤立的亚暴期间识别所有天空图像中的极光流光。一种叫做“点过程统计”的技术将被用来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，以研究磁尾中突发流动与极光特征之间的关系。进一步的目标将是调查在亚暴发生时极光珠是否持续存在。极光珠被认为是由磁尾膨胀的不稳定性产生的结构。一个积极的结果将暗示气球不稳定性在亚暴发生中可能起作用。

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.