三维行星际磁场中太阳高能粒子的扩散机制研究

Solar energetic particles (SEP), which are charged energetic particles occasionally emitted by the Sun, are harmful to the electronic components on satellites and the health of astronauts working in space, so they have become an important aspect in affecting solar-terrestrial space environment and space weather. With combination of numerical simulations and spacecraft observations, in this project we will investigate the transport processes and relevant diffusion mechanism of SEP in three-dimensional interplanetary magnetic fields, and provide new insights to quantitatively explain the observational phenomena and lay the physical bases for establishing forecast model of SEP events. Firstly, by fitting numerical simulations to multi-spacecraft observations, we will determine the perpendicular diffusion coefficient of SEP transporting in three-dimensional interplanetary magnetic fields, and by means of perpendicular diffusion mechanism, we will revisit the rigidity dependence of the parallel mean free path of SEP. Secondly, we will demonstrate the effects of the spatial distribution of the particle injection strength inside the solar source region on the propagation of SEP in the interplanetary magnetic fields. In addition, based on our previous theoretical studies, we will investigate the inherent relations between the mean free path of SEP and interplanetary conditions such as the magnetic fields and solar wind, and present analytical formulae and direct methods to quickly and accurately determine the mean free path of SEP. We will also apply the analytical formulae and direct methods to observational and forecasting research of SEP events.

太阳高能粒子(SEP)是由太阳喷发出来的高能带电粒子，对于在太空中作业的宇航员和卫星上的电子元器件均构成严重的威胁，成为影响日地空间环境和空间天气的一个重要因素。本项目拟结合数值模拟和飞船观测，研究三维行星际磁场中太阳高能粒子的传播过程及其扩散机制，为定量解释相关观测现象提供新思路，为构建太阳高能粒子事件预报模式奠定物理基础。首先，通过将数值模拟结果与多个飞船观测数据进行比对，确定三维行星际磁场中太阳高能粒子传播过程的横向扩散系数；引入横向扩散机制重新厘定太阳高能粒子平行平均自由程对于粒子刚度的依赖关系。其次，阐明太阳源区粒子注入强度空间分布对行星际磁场中高能粒子传播过程的影响。此外，本项目拟在前期理论研究工作基础上，探讨太阳高能粒子平均自由程与磁场、太阳风等行星际条件的内在联系，建立快速、准确确定太阳高能粒子平均自由程的解析公式和直接方法，并将其应用到太阳高能粒子事件的观测和预报研究中。

太阳高能粒子是由太阳喷发出来的高能带电粒子。太阳高能粒子对在太空中作业的宇航员和卫星上的电子元器件均构成严重威胁，因而成为影响日地空间环境和空间天气的重要因素。本项目对太阳高能粒子在三维行星际磁场中的扩散机制与传播过程开展了深入研究，获得了重要进展和成果。主要包括：（1）提出了一种确定太阳高能粒子平均自由程的直接方法；（2）基于理论模型和飞船观测，对多个典型太阳高能粒子事件的扩散系数开展了比对研究；（3）计算了叠加静磁湍流的大尺度非均匀引导磁场中宇宙线的平均自由程；（4）发现了太阳高能粒子在日球层的“相对经度”东-西非对称分布现象并分析了其物理机制；（5）研究了随日球纬度变化的太阳风速度及日球磁场对宇宙线平行、垂直和漂移扩散系数的重要作用；（6）通过对太阳高能粒子多维传播方程的数值模拟，研究了垂直扩散机制对行星际空间反向流动粒子束现象形成的重要作用。受本项目部分资助，已在本领域国际主流期刊上发表6篇论文。本项目研究成果对于深入理解太阳高能粒子在行星际空间中的传播与分布具有重要意义，并有助于深入理解日地联系。