太阳爆发活动源区三维非势磁场重构的MHD方法研究

Space-weather events originate from solar eruptive activities such as solar flares and coronal mass ejections (CMEs), and determining the three-dimensional (3D) structure of the coronal fields associated with the eruptions is key to understanding how the eruptions are produced. Routine measurements of the solar magnetic field vector are traditionally carried out in the photosphere, while the coronal fields are usually extrapolated from photospheric magnetogram basing on some non-potential models. The currently available methods for coronal field extrapolation have only limited success when applied to real solar data, so further improvements in modeling techniques are urgently needed, especially considering that high-resolution, large field-of-view magnetograms are routinely available from the Solar Dynamics Observatory (SDO). In this proposal, we will develop a new high-accuracy and high-performance extrapolation code for the 3D coronal fields to meet such need. This project takes advantage of our new-developed CESE-MHD method in general curvilinear coordinates with AMR (adaptive mesh refinement) grid technology and rich experience in developing large-scale MHD applications. We plan to apply the new method to the high-quality vector magnetograms from SDO/HMI to study the 3D magnetic topology of the active regions and the magnetic mechanism of solar eruptions. Furthermore, we will implement a first reconstruction of the global coronal non-potential field using the full disk vector map from SDO. The reconstructed global field can be used to initialize 3D MHD models that simulate the solar storms from corona to interplanetary for space-weather forecasting.

空间天气事件起因于太阳爆发活动如耀斑和CME，理解太阳爆发活动的关键在于获得源区的三维磁场。由于目前日冕磁场尚难以直接测量，人们普遍采用磁场重构的办法将易观测的光球面二维磁场外推到三维日冕。近年来高精度大视场的矢量磁图不断出现，给传统的重构方法带来了极大挑战，因此发展高精度高效率的磁场重构技术来分析这些大型观测资料显得尤为紧迫和必要。本项目将基于MHD演化方法，充分利用我们在高精度数值格式、并行自适应曲线网格以及开发大型MHD应用的技术优势和丰富经验，建立一种精确高效的日冕活动区三维磁场重构的新方法，并实现首个基于矢量磁图的全球面日冕非势性磁场的重建。该方法将应用于SDO/HMI的高质量、大视场及全日面矢量磁图，来研究太阳爆发源区局部和全局的三维磁拓扑结构，以理解爆发活动的磁场机制；并可用重构的三维非势磁场初始化大型的太阳风暴三维模式，为建立基于物理的空间天气预报模式服务。

太阳爆发活动（如耀斑和日冕物质抛射）是导致灾害性空间天气的主要驱动源头。虽然爆发现象表现的形式丰富多样，但从本质而言，它们都是积蓄了充分自由磁能量的日冕磁场系统突发失衡的过程。因此理解各种太阳爆发的关键在于获得其源区的三维磁场。但是日冕磁场尚难以直接测量，人们普遍采用磁场重建的办法将易观测的光球面（即太阳表面）磁场外推的到三维日冕磁场。近年来随着高精度大视场的光球矢量磁图的出现（特别是如Hinode/SOT，SDO/HMI的观测数据），许多传统的日冕磁场重建方法受到了极大的挑战，因此发展高精度高效率的磁场重构技术来分析这些大型观测资料显得尤为紧迫和必要。本项目成功开发了非线性无力场外推方法CESE-MHD-NLFFF，该方法基于MHD弛豫原理，充分利用了高精度数值格式的技术优势，首次将并行自适应的网格技术应用到了日冕磁场外推，实现了全球面日冕非势性磁场的重建；此外本项目还提出了一种新的矢量磁图预处理方法以有效剔除光球磁场中的洛伦茨力。这些技术在计算精度和效率上都达了国际最佳水平，受到太阳物理研究领域内同行的公认，并开始被相关研究者所应用。基于最新的SDO/HMI矢量磁图，利用该方法可以有效获得太阳爆发源区局部甚至全局的三维磁结构，计算磁拓扑特征、电流分布和磁能量等参数，以帮助理解爆发活动的磁场机制；并可用重构的三维非势磁场初始化大型的太阳风暴三维模式，以进一步模拟接近真实的日地空间环境，为建立基于物理的空间天气预报模式服务。