Embedding Force-Free Flux Ropes in Potential Magnetic Fields

太阳爆发现象，如日冕物质抛射（cme）和耀斑，会造成一些最严重的空间天气影响。它们被认为是由太阳日冕中磁能的爆炸释放造成的，目前还不能直接测量日冕中的磁场。这一研究项目有望对空间天气的物理驱动因素进行更好的建模和更深入的了解。基于物理的对日冕物质抛射的根本原因的理解，最终可以更好地预测空间天气事件，从而可以采取缓解措施，保护人类和技术资产。要模拟太阳喷发现象，关键是要有一种有效的方法，从光球磁场数据中数值构造喷发前的结构。与现有的方法（如非线性无力场重建或通量绳插入）相比，该项目将开发的新方法预计将具有很强的竞争力，特别是在效率和对所得通量绳参数的控制方面。这项调查是及时的、可行的，并且与美国国家科学基金会的太阳地球研究计划直接相关，该计划“支持对各种形式的能量由太阳产生、输送到地球并最终沉积在陆地环境中的过程的研究”。因此，该项目支持AGS部门在发现、学习、多样性和跨学科研究方面的战略目标。迄今为止，在许多这些模型中，分析或半分析通量绳模型被用作喷发的基础。这个为期3年的项目旨在构建嵌入环境势场的柔性形状无力通量绳的解析近似解，其光球通量分布与观测场相匹配。近平衡解析解将通过线系MHD模拟进一步放宽，以达到近似的数值稳定平衡，作为实际CME事件的MHD模拟（进一步驱动）的初始状态。该项目将改进目前PI开发的Titov-Demoulin （TD）无力磁通绳模型，以允许磁通绳复杂形状/路径的灵活性，并保留观测磁图中的磁通分布。基于这种技术的喷发前构造计算将是简单、高效的，并且得到的模型将明显比目前使用的CME模拟更准确。作为这项研究的一部分，项目组将提供公式和生成平衡通量绳的数值代码，这样来自太阳-日球圈社区的其他研究人员将能够在他们自己的代码中使用这些模型进行实验。

Solar eruptive phenomena, such as Coronal Mass Ejections (CMEs) and flares, cause some of the most severe space-weather effects. They are believed to result from an explosive release of magnetic energy in the solar corona, where the magnetic field cannot at present be measured directly. This research project is expected to lead to a better modeling and deeper understanding of the physical drivers of space weather. A physics-based understanding of the underlying cause(s) of CMEs can eventually lead to a better forecasting of space-weather events, which may allow mitigating steps to be taken to protect human and technological assets. To model solar eruptive phenomena, it is critical to have an efficient method for numerically constructing pre-eruptive configurations from photospheric magnetic data. The new method to be developed over the course of this project is expected to be highly competitive compared to the existing ones, such as the nonlinear force-free field reconstruction, or flux-rope insertion, especially in terms of the efficiency and control of the resulting flux-rope parameters. This investigation is timely, feasible, and directly related to the NSF's Solar Terrestrial Research Program that "supports research on the processes by which energy in diverse forms is generated by the Sun, transported to the Earth, and ultimately deposited in the terrestrial environment." Therefore, the project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research. To date, analytical or semi-analytical flux-rope models are being used as the basis for the eruption in many of these models. This 3-year project aims to construct analytically approximate solutions of a force-free flux rope of flexible shape embedded in an ambient potential field, with photosphere flux distribution matching the observed fields. The near-equilibrium analytic solution will be relaxed further with line-tied MHD simulations to reach an approximate numerical stable equilibrium as the initial state for MHD simulations (with further driving) of realistic CME events. The project will improve upon the current Titov-Demoulin (TD) force-free flux rope model the PI has developed to allow for the flexibility of complex shapes/paths of the flux rope and preserve the flux distribution in the observed magnetograms. The computation of pre-eruptive configurations based on this technique will be simple, highly efficient, and the resulting model will be significantly more accurate than those used in CME simulations so far. As part of this investigation, the project team will provide formulas and a numerical code for producing equilibrium flux ropes, so that other researchers from the solar-heliospheric community will be able to experiment using these models in their own codes.