A Data-Driven Approach to Characterizing the Structure and Processes of Saturn's Magnetosphere

卡西尼号在环绕土星的轨道上运行了13年，收集了大量关于土星全球磁场和等离子体环境、土星环和卫星的数据，这些数据改变了我们对土星系统复杂本质的理解。土星磁层的边缘，称为磁层顶（MP），以及超越它的弓形激波（BS）是行星科学家特别感兴趣的，因为这些边界在等离子体的能量和通过湍流加热、波粒相互作用和磁重联等过程的传输中起着重要作用。研究这些基本过程需要一个交叉的目录。然而，一个非常具有挑战性的方面是人工识别卡西尼号航天器所做的数千个边界交叉点，特别是通过磁层顶电流层的精确过渡。我的工作旨在利用多仪器数据集的时间序列分析、磁场数据的最小方差分析、能量分布函数的矩和土星环境的其他物理知识来自动检测这些边界。此外，这些技术与机器学习中的数据密集型算法（如XGBoost）相结合，通过监督学习进行不确定性量化的卷积神经网络可以更有效地检测BS和MP交叉。有了这个标准化的交叉表，就可以研究磁层有趣的结构和过程。例如，土星MP的电子加热与磁重联之间的关系，土星磁鞘中镜像模式不稳定性的表征，改进了对土星MP附近罕见的“缓冲”区域的搜索，迄今为止只发现了5个，而木星日侧MP附近则持续发生。

The Cassini mission spent 13 years in orbit around Saturn collecting a wealth of data about its global magnetic and plasma environment, its rings and moons, which shifted our understanding of the complex nature of the Saturnian system. The edge of Saturn's magnetosphere, called the magnetopause (MP), and beyond that the bow shock (BS) are of particular interest to planetary scientists due to the role these boundaries play in plasma energization and transport via processes like turbulent heating, wave-particle interaction and magnetic reconnection. A catalogue of crossings is needed to study these fundamental processes. However, a very challenging aspect is the manual identification of thousands of boundary crossings made by the Cassini spacecraft, particularly the precise transition across the magnetopause current layer.My work aims to automate the detection of these boundaries using time series analysis of multi-instrument datasets, minimum variance analysis of magnetic field data, moments of energy distribution functions and other physical knowledge of Saturn's environment. In addition, these techniques are ensembled with data-intensive algorithms in machine learning such as XGBoost, convolutional neural networks with uncertainty quantification via supervised learning for more efficient detection of BS and MP crossings. With this standardized crossing list, interesting structures and processes of the magnetosphere can be studied. For example, the relation between electron heating at Saturn's MP and magnetic reconnection, characterization of mirror mode instability in Saturn's magnetosheath, improving the search of rare 'cushion' regions near Saturn's MP of which only 5 have been found to date, in contrast to a persistent occurrence near Jupiter's dayside MP.