Collaborative Research: Flow Channel Control of Substorm Expansion Phase Spatial Coverage and Duration

空间天气描述了太阳和地球之间空间环境的变化。空间天气通常表现为亚暴，即美丽的极光显示伴随着空间中的电流，这种电流会影响轨道和地球上的系统和技术，如航天器和配电系统。亚暴在时间上（几小时）和空间上（极区）是局部的。该项目将促进对空间天气干扰的理解，从而使社会受益，这些干扰会对空间和易受影响的地面系统产生重大影响。更具体地说，目前的空间天气预报在长时间尺度上具有一定的有效性，但严重缺乏预测短期（如亚暴和流子时间尺度）扰动的发生、持续时间和空间覆盖的能力。这个项目直接针对这个问题，通过研究是什么决定了个体干扰的空间和时间发展。该项目还将为协调使用地面能力来攻击磁层-电离层耦合物理的主要方面树立进一步的先例。该团队将促进加州大学洛杉矶分校、波士顿大学和宾夕法尼亚州立大学相关研究活动之间的研究伙伴关系和协调，以宣传和开发新的方法，使国家科学基金会观测设施的回报最大化。这项研究还将继续为加州大学洛杉矶分校的新生研讨会（“菲亚特Lux”）课程“北极光的秘密：地球的极光”提供材料和动力，该课程激发了一群才华横溢、多样化和热情的学生，导致了本科生的研究项目。亚暴对空间天气的影响不仅取决于其峰值瞬时强度，还取决于其高度可变的空间范围和持续时间。尽管它们非常重要，但由于缺乏对可能是重要因素的想法，空间范围和持续时间很少受到关注。最近人们已经知道，在极光椭圆（地球地磁北极上方的极光环）内从高纬度向低纬度移动的带电粒子流动通道是极光椭圆的一个重要特征，也是亚暴发生的原因。本研究项目将重点研究亚暴发生后这些流动通道的作用，并评估它们是否在控制亚暴局地时间范围、向极扩展和持续时间方面发挥关键作用。由于流动通道相关的流动和场向电流沿着连接磁层和电离层的磁力线绘制，研究小组将主要使用美国国家科学基金会资助的（和其他一些）雷达和全天成像仪进行评估，这些雷达和成像仪极大地改善了对北美电离层流动和极光（代表向上的场向电流）的测量。这使得该团队可以进行随时间的二维测量，这是稀疏航天器无法做到的。研究人员还将利用一项重大的新发展，即从雷达数据中确定二维流量。这个项目的目标是建立：1。相对于起始弧变亮的方位角膨胀的等离子体流动是否与Rice对流模型所预测的起始流通道的低熵等离子体方位角膨胀的结果相一致？2. 在控制亚暴扩展的纵向发展过程中，极光凸起外的后发流通道起什么作用？3. 指向活跃的亚风暴极光凸起的极地边界的极帽流通道在控制进一步向极地扩展和亚风暴扩展阶段极光活动的持续时间方面是否重要？4. 从极光极边界开始的膨胀相扰动的纵向范围和持续时间是否由极帽流通道控制？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。

Space weather describes the variations in the space environment between the sun and Earth. Space weather often manifests as substorms, where a beautiful auroral display is accompanied by an electrical current in space which can impact systems and technologies in orbit and on Earth, such as spacecrafts and power distribution systems. The substorm is localized in time (a few hours) and space (polar region). This project will benefit society by advancing understanding of space weather disturbances, which significantly affect space and susceptible ground systems. More specifically, current space weather forecasting has some validity over long time scales, but severely lacks ability to predict onset, duration, and spatial coverage of short term (e.g., substorm and streamer time scales) disturbances. This project is directly aimed at this issue by examining what determines spatial and temporal development of individual disturbances. The project will also set further precedents on coordinated use of ground-based capabilities to attack major facets of coupled magnetosphere-ionosphere physics. The team will promote research partnerships and coordination between the relevant research activities at UCLA, Boston University, and Penn State to publicize and develop new approaches for maximizing return from NSF observing facilities. The research will also continue to provide material and motivation for a UCLA freshman seminar (“Fiat Lux”) course at UCLA “Secrets of the Northern Lights: The Earth’s aurora” that has stimulated a talented, diverse, and enthusiastic group of students, leading to undergraduate research projects.The Space Weather effects of a substorm depend not only on its peak instantaneous strength, but also on the highly variable spatial extent and duration. Despite their significant importance, the spatial extent and duration has received little attention due to the lack of ideas on what may be the important factors. It has recently become known that flow channels of charged particles within the auroral oval (the ring of aurora above the Earth’s geomagnetic North Pole) that move from higher to lower latitude are a crucial feature of the oval and are responsible for the onset of a substorm. This research project will focus on the role of these flow channels that occur after substorm onset and evaluate whether they play a crucial role in controlling the local time extent, the poleward expansion, and the duration of the substorm. Since flow channel related flows and field-aligned currents map along magnetic field lines that connect the magnetosphere and ionosphere, the team will make evaluation using primarily the NSF funded (and some other) radars and all-sky imagers that have greatly improved measurements over North America of ionospheric flows and aurora (which represent upward field-aligned currents). This allows the team to make two-dimensional measurement versus time, which cannot be done with sparse spacecraft. The investigators will also make use of a major new development in 2-D flow determination from radar data. The goals of this project are to establish: 1. Are plasma flows relative to the azimuthal expansion of the brightening of the onset arc consistent with that brightening expansion being the result of azimuthal expansion of the low entropy plasma from the onset flow channel as predicted by the Rice Convection Model? 2. What is the role of post-onset flow channels outside the auroral bulge in controlling the longitudinal development of substorm expansion? 3. Are polar cap flow channels directed toward the poleward boundary of the active substorm auroral bulge important in controlling further poleward expansion and the duration of substorm expansion-phase auroral activity? 4. Is the longitudinal extent and duration of the expansion-phase-like disturbances that initiate from the auroral polar boundary controlled by polar cap flow channels?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.