Revisiting the Stormtime Magnetosphere-Ionosphere Coupling: Enhancement of the Dawnside Auroral Electrojet

地磁风暴是地球空间中最强烈的一类扰动，是空间天气的关键目标。空间天气是空间科学的一个相对较新的领域，其目的是了解和预测面向空间的事件，这些事件会影响社会基础设施，如一般的卫星操作、GPS系统和电网，有时甚至会危及人类健康（例如，飞机和航天机组人员的辐射暴露）。本文研究了风暴时电离层电流及其在磁层中的来源。在地磁风暴期间，电离层电流增强，特别是在高纬度地区，部分原因是太阳风向磁层输入的能量增加，部分原因是强烈的极光降水增强了电离层电导。此外，在一些严重的风暴期间，电离层电流向赤道向下移动到美国大陆的北部，在历史上强烈的风暴期间，电离层电流向南移动。众所周知，此类事件是对美国电网的威胁。本研究试图从观测上描述和理解当地时间黎明部分的风暴时电流系统，在那里地面磁扰动通常是最大的。预计该项目的成功实现将为地球空间风暴时电动力学带来新的见解，并有助于建立预测危险事件的模型。本研究项目的目标是黎明侧极光电喷流（AEJ）的增强，该增强最近被确定为风暴时地面磁降（风暴主阶段的一个特征）的黎明-黄昏不对称的合理原因。该电流系统在黎明区域的限制表明，该AEJ增强是三维电流系统的电离层部分，即黎明侧楔形电流（DWC）系统。然而，它的产生过程在很大程度上是未知的。一种假设是(A) DWC系统是一个强烈的亚风暴流楔向黎明倾斜，另一种观点是(B)它的形成是因为黎明侧电离层电导在强烈的全球对流存在下增强。本项目试图从以下五个方面对DCW的发展特征进行观察研究：(1)DCW发生的内外部条件；(2)时空尺度；(3)其发展和预处理的时间顺序；(4)双极化和粒子注入；(5)等离子体薄片对流。该团队将系统地选择具有SuperMAG指数的事件，并将处理(1)各种内部和外部参数的概率密度函数，(2)和(3)磁扰动和极光的极性分布，(4)近地磁层中的磁场和高能粒子通量测量，以及(5)等离子层中的对流测量。我们根据上述两个假设(A)和(B)批判性地评估结果。通过揭示DWC系统形成的过程，本项目将把我们对风暴动力学的理解提升到一个新的水平。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The geomagnetic storm is the most intense class of disturbances in geospace, and the critical target of space weather. Space weather is a relatively new area of space science, which aims at understanding and predicting space-oriented events that impact societal infrastructures such as satellite operations in general, GPS system, and power grids, and sometimes they even risk human health (e.g., radiation exposure for aircraft and space crews). This study investigates the stormtime ionospheric current and its source in the magnetosphere. During geomagnetic storms, the ionospheric current intensifies especially in high latitudes, partly because the energy input from the solar wind to the magnetosphere increases, and partly because intense auroral precipitation enhances the ionospheric conductance. Moreover, during some severe storms, the ionospheric current moves equatorward down to the northern part of the continental US, and farther south during historically intense storms. Such events are widely known as a threat to US power networks. This study seeks to observationally characterize and understand a stormtime current system in the dawn local time sector, where ground magnetic disturbances very often become the largest in magnitude. It is expected that the successful achievement of this project brings new insights into stormtime electrodynamics in geospace and contributes to building models to predict hazardous events.The target of this research project, the enhancement of the dawnside auroral electrojet (AEJ), which was recently identified as a plausible cause of the dawn-dusk asymmetry of stormtime ground magnetic depression, a characteristic feature of the storm main phase. The confinement of this current system in the dawn sector suggests that this AEJ enhancement is an ionospheric segment of a 3D current system, the dawnside wedge current (DWC) system. However, its generation process is largely unknown. One hypothesis is that (A) the DWC system is an intense substorm current wedge skewed dawnward, and an alternative idea is that (B) it forms because the dawnside ionospheric conductance enhances in the presence of intense global convection. This project seeks to observationally examine the characteristics of the DCW development from five viewpoints: (1) internal and external conditions for its occurrence; (2) spatial and temporal scales; (3) time sequence of its development and preconditioning; (4) dipolarization and particle injection; (5) plasma sheet convection. The team will systematically select events with SuperMAG indices, and will address (1) with the probability density functions of various internal and external parameters, (2) and (3) with polar distributions of magnetic disturbances and aurora, (4) with magnetic field and energetic particle flux measurements in the near-Earth magnetosphere, and (5) with convection measurements in the plasma sheet. We critically evaluate the results in terms of the aforementioned two hypotheses, (A) and (B). By revealing the process responsible for the formation of the DWC system, the present project will advance our understanding of storm dynamics to a new level.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.