太阳磁场模型、拓扑结构和磁螺度的研究

The activities in the solar atmosphere have a significant impact on the environment of the interplanetary space and the Earth. In order to understand various solar activities and phenomena, such as coronal mass ejections, flares, and filaments, we have to study the three dimensional magnetic field in the solar atmosphere. However, there are still difficulties in observing the magnetic field in the solar upper atmosphere. We are going to construct three dimensional magnetic field models using the nonlinear force-free field model, and analyze the magnetic topology and magnetic helicity. This is because that the magnetic topology has a close relationship with magnetic reconnection, and the magnetic helicity is closely related to magneto-hydrodynamic instabilities. We will compute magnetic null points, bald patches, magnetic dips, and quasi-separatrix layers in a magnetic field, and calculate the relative magnetic helicity using a finite volume method, a discrete flux tube method, and helicity flux integration method. If the magnetic topology and magnetic helicity could be determined accurately, we would understand magnetic reconnection and magneto-hydrodynamic instabilities more deeply, which is also important for us to interpreting and predicting solar activities and phenomena.

太阳大气中的活动现象会对日地空间和地球环境造成严重干扰。为了理解日冕物质抛射、耀斑和暗条等太阳爆发活动和现象，我们必须研究太阳三维磁场结构。然而，高层大气磁场的观测仍然存在着种种困难。我们准备使用非线性无力场模型构造三维磁场模型，进而分析磁场的拓扑结构和磁螺度，这是因为磁场拓扑结构和磁重联密切相关，而磁场螺度则和磁流体力学不稳定性息息相连。我们准备计算磁场的磁零点、秃斑、磁凹陷和准分界面；使用有限体积法、离散磁流管法和磁螺度通量积分法计算相对磁螺度。如果磁场拓扑结构和磁螺度可以准确的确定，我们就可以更加深入地理解磁重联和磁流体力学不稳定性，这对我们解释和预测太阳爆发活动和现象具有重要的意义。

太阳爆发活动产生的灾害性空间天气会对地球环境造成严重破坏。为了理解日冕物质抛射等太阳爆发活动，我们需要研究太阳三维磁场模型、拓扑结构及其磁场螺度。本项目围绕这一主题开发了新的非线性无力场模型和数据驱动磁流体力学模拟方法，并且把这些方法应用到实际太阳观测数据中，研究了磁场拓扑、磁螺度和太阳活动现象的关系。本项目的重要成果包括开发了磁场建模程序库，发布在开源程序网站GitHub上。这个程序库提供了一系列计算磁场模型、磁场拓扑和磁场螺度的方法。在《自然·通讯》期刊发表两篇文章，分别提出了非理想化速度计算日冕加热率的模型和磁绳非轴对称性引起失败爆发的机制。这些模型和数值方法对于我们理解太阳爆发活动的物理机制，构造基于物理模型的空间天气预报平台具有重要的科学意义和应用价值。