GEM: Onset and Consequences of Reconnection in the Magnetotail

该项目解决了一些引人注目的问题，这些问题一直是关于严重空间天气活动的诱因的持续辩论和争议的主题。该团队将使用最先进的3D动力学粒子在细胞(PIC)模型来跟踪地球磁尾从稳定形态到爆炸性磁重联的演变，该模型已被修改为在千万亿级计算机上高效运行。实际上，磁重联是磁力线的断裂和重新连接，伴随着能量的爆炸性释放，对太空中的“恶劣天气”的发展至关重要。该项目的另一个重要特点是，模拟将及时继续，以跟踪爆炸能量释放后磁尾的演变。这使得能够调查与空间风暴发展有关的一些观察到的现象--其中一些是最近才认识到的。该项目在提供变革性新知识方面具有很高的潜力。了解在完全不同的空间和时间尺度上发生的过程之间的相互作用，是理解从恶劣空间天气到龙卷风、火山喷发到地震等极端事件发展的一项重大挑战。该项目的目标和方法与NSF极端事件预测和抵御极端事件(PREEVENTS)计划的重点密切一致，该计划是上述工作的共同资金来源。该项目将支持培养一名博士后，为未来的科学劳动力做出贡献。这项工作的结果将对更广泛的科学界的一系列学科领域感兴趣，因为磁重联发生在空间、天体物理和实验室等离子体中。从长远来看，关于空间风暴期间爆炸能量释放的触发因素的新知识将改善空间天气预测。通过利用千万亿级计算机重组PIC模型，可以在理解磁重联的爆炸性开始及其原因方面取得进展。PIC模型跟踪带电粒子通过固定网状点计算的自洽电磁场时的路径。为了减少计算机必须跟踪的极大数量的粒子，并使计算变得容易处理，模拟使用了计算超级粒子，每个超级粒子可能代表数百万带电粒子。本项目中使用的VPIC模型是一种最先进的、高性能的3D全动态粒子单元模型。它是世界上速度最快、优化程度最高、功能最强大的PIC型号之一。在PB级计算机上，使用该代码进行的模拟已超过3万亿个粒子和150亿个细胞。一个重要的方面是，该模式能够模拟发生重联的微尺度扩散区的不稳定性和动力学，同时在更大尺度上观察扩散区与磁尾之间的耦合，这对全球风暴发展具有重要意义。

This project addresses compelling questions that have been the subject of continuing debate and controversy regarding the triggers of severe space weather activity. The team will follow the evolution of the Earth's magnetotail from a stable configuration to the onset of explosive magnetic reconnection using a state-of-the-art 3D kinetic particle-in-cell (PIC) model that has been modified to run efficiently on petascale computers. Magnetic reconnection is, in effect, the breaking and reconnecting of magnetic field lines, which is accompanied by an explosive release of energy, and is critical to the development of "severe weather" in space. An important additional feature of the project is that the simulations will be continued in time to follow the evolution of the magnetotail after the explosive energy release. This enables investigation of a number of observed phenomena connected to the space storm development - some only recently appreciated. This project has a high potential for delivering transformative new knowledge. Gaining knowledge about the interactions between processes that occur on disparate spatial and temporal scales is a major challenge in understanding the development of extreme events ranging from severe space weather to tornadoes to volcanic eruptions to earthquakes. The objectives and methodology in this project are closely aligned with the focus of the NSF Prediction of and Resilience against Extreme Events (PREEVENTS) program, which is co-funding the work described above. The project will support the training of a postdoctoral student, contributing to the future scientific workforce. The results of this work will be of interest to a range of discipline areas in the broader scientific community because magnetic reconnection occurs in space, astrophysical, and laboratory plasmas. In the longer term, new knowledge about the triggers of explosive energy release during space storms will improve space weather prediction.Progress in understanding the explosive onset of magnetic reconnection and its causes is enabled through the restructuring of PIC models to take advantage of petascale computers. PIC models follow the paths of charged particles as they move through self-consistent electromagnetic fields computed at points within a fixed mesh. To reduce the extremely large number of particles that the computer must follow and make the calculation tractable, the simulation uses computational superparticles, each of which may represent millions of charged particles. The VPIC model used in this project is a state-of-the-art, high performance, 3D fully kinetic particle-in-cell model. It is one of the fastest, most optimized, and most capable PIC models in the world. Simulations using this code have exceeded 3 trillion particles and 15 billion cells on petascale computers. An important aspect is that the model is able to simulate the instabilities and dynamics in the micro-scale diffusion region where reconnection occurs, while at the same time viewing the coupling between the diffusion region and the magnetotail at the larger scales important in the global storm development.