Investigation of the Causes and Effects of the Storm-Time Ion Ring Current Decay

地球环电流是一种在地球周围流动的电流，距离大气层数千英里。环电流是主要的电流系统之一，它控制着轨道卫星运行的大气层以上空间的条件。这种电流可能会发生几个数量级的突然变化，导致地球表面磁场的全球减弱，即地磁风暴。因此，风暴时的环电流与有害的空间天气效应有关，这激发了对其形成、动力学和衰减的研究。当环电流在数小时到数天的时间尺度上衰减时，它的能量通过损耗过程释放到空间和大气中，损耗过程对这种衰减的贡献仍然是与环电流有关的悬而未决的问题之一。本项目旨在研究环电流离子风暴时间衰减的原因和影响，环电流离子是环电流的主要载流子。所提出的工作可以大大提高我们对地球环电流动力学的认识，包括它的空间天气效应和耦合空间环境。此外，作为拟议活动的一部分，高中生将通过参加美国宇航局戈达德太空飞行中心的美国宇航局暑期实习计划，受益于最先进的科学研究。在风暴恢复阶段，当环电流在数小时到数天的时间尺度上衰减时，其能量通过电荷交换、库仑碰撞、场线曲率散射、与等离子体波的共振相互作用以及向日侧磁层顶漂移损失等损失过程被释放到空间、大气和等离子层。这个项目解决了关于环电流衰减的未解决的科学问题。该方法将包括数值模拟和观测数据验证。本研究的主要建模工具将是综合内磁层-电离层（CIMI）模型。这个最先进的动力学模型考虑了环电流和内磁层中其他等离子体种群之间的必要耦合。将进行实际风暴事件的模拟研究，以量化个别过程如何导致环电流损失，以及相关的离子降水如何影响电离层电导及其对磁层的反馈。这项建模工作的预期结果是对不同损失机制的作用进行系统的量化。要实现这一量化，需要对风暴时间环电流进行模拟研究，并考虑到所有已确定的损失机制。此外，已知内磁层对不同太阳风驱动产生的风暴有不同的响应，即由日冕物质抛射（cme）或同向旋转相互作用区（CIRs）驱动。因此，本研究将系统分析CME和CIR驱动风暴中不同离子损失过程的相对作用及其对磁层-电离层耦合系统的影响。因此，这项研究将通过提供在太阳风驱动的不同背景下环电流衰减期间和导致环电流衰减的物理过程的全面视图来推进我们目前的知识。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 terrestrial ring current is an electric current flowing around the Earth, thousands of miles above the atmosphere. The ring current is one of the principal current systems that control conditions in the space above the atmosphere where orbiting satellites operate. Abrupt changes of several orders of magnitude in this current may occur, responsible for global decreases in the Earth's surface magnetic field, known as geomagnetic storms. The storm-time ring current is thus associated with harmful space weather effects, which motivates the study of its formation, dynamics, and decay. As the ring current decays on time scales of hours to several days, its energy is released into space and the atmosphere by loss processes, whose contribution to this decay remains one of the outstanding questions related to the ring current. This project aims to study the causes and effects of the storm-time decay of the ring current ions, which are the main carriers in the ring current. The proposed work can significantly advance our knowledge of the dynamics of the Earth's ring current, including its space weather effects and the coupled space environment. Moreover, as part of the proposed activities, high school students will benefit from state-of-the-art science research by participating in the NASA summer internship program at NASA Goddard Space Flight Center. As the ring current decays on time scales of hours to several days during the storm recovery phase, its energy is released into space, the atmosphere, and the plasmasphere by means of loss processes such as charge exchange, Coulomb collisions, field line curvature scattering, resonant interactions with plasma waves, and drift out loss to the dayside magnetopause. This project addresses unresolved science questions regarding the decay of the ring current. The methodology will consist of numerical simulations and validation with observational data. The primary modeling tool in this investigation will be the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. This state-of-the-art kinetic model considers necessary couplings between the ring current and the other plasma populations in the inner magnetosphere. Simulation studies of actual storm events will be performed to quantify how individual processes result in ring current losses and how the associated ion precipitation affects the ionospheric conductance and its feedback to the magnetosphere. The expected result from this modeling work is a systematic quantification of the roles of the different loss mechanisms. Achieving this quantification requires an investigation that models the storm-time ring current, accounting for all the identified loss mechanisms. Furthermore, it is known that the inner magnetosphere responds distinctively to storms produced by different solar wind drivers, i.e., driven by coronal mass ejections (CMEs) or by co-rotating interaction regions (CIRs). The proposed research will thus perform a systematic analysis of the relative roles of the different ion loss processes during storms of CME and CIR drivers and the impacts on the magnetosphere-ionosphere coupled system. Consequently, this study will advance our current knowledge by providing a comprehensive view of the physical processes during, and leading to, the decay of the ring current in different contexts of solar wind driving.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.