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，在这种情况下，美丽的极光显示伴随着空间中的电流，这可能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(几个小时)和空间上(极地)是局部性的。该项目将通过增进对空间天气扰动的了解而造福社会，因为空间天气扰动对空间和易受影响的地面系统有重大影响。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(例如亚风暴和流光时间尺度)扰动的开始、持续时间和空间覆盖的能力。该项目直接针对这一问题，审查了决定单个干扰的空间和时间发展的因素。该项目还将在协调利用地面能力打击磁层-电离层耦合物理的主要方面方面开创进一步的先例。该小组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，以宣传和开发从NSF观测设施获得最大回报的新方法。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·勒克斯)课程提供材料和动机，该课程名为《北极光的秘密：地球的极光》，激发了一群有才华、多样化和热情的学生，导致了本科生的研究项目。亚风暴的空间天气效应不仅取决于其峰值瞬时强度，还取决于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几乎没有受到关注。最近人们知道，极光椭圆形(地球地磁北极上方的极光环)内从较高纬度移动到较低纬度的带电粒子的流动通道是椭圆形的一个重要特征，是引发亚暴的原因。这项研究项目将集中在亚暴发生后出现的这些气流通道的作用，并评估它们是否在控制亚暴的当地时间范围、向极地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对齐电流沿着连接磁层和电离层的磁力线绘制地图，该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，这些雷达和全天成像仪极大地改善了北美地区对电离层流动和极光(代表向上的场对齐电流)的测量。这使得该团队能够进行与时间相关的二维测量，而这是稀疏航天器无法完成的。调查人员还将利用雷达数据确定二维流动的一项重大新发展。这个项目的目标是建立：1.相对于爆发弧亮化的方位向扩展的等离子体流动是否与莱斯对流模型所预测的亮化扩张是低熵等离子体从起始流道方位向扩张的结果一致？2.爆发后的流道在控制亚暴扩张的纵向发展中所起的作用是什么？3.指向活跃的亚暴极光凸起极地边界的极冠流动通道对于进一步控制极地扩张和亚暴扩张相极光活动的持续时间是否重要？4.纵向的极光扩张阶段极光活动从极地帽流通道控制的极光极地边界开始的扩展相类扰动的范围和持续时间？这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势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.