冕环与开放场重联驱动太阳风起源的数值模拟研究

The origin mechanism of solar wind remains as one of the key topic in the space physics and space exploration. Present models mostly assume that solar wind flows outward continuously from the photosphere through the chromosphere to the corona. According to new observational results, Fisk et al., (1999, 2003) and Tu et al., (2005a, b) proposed origin model as driven by magnetic reconnection (hereafter be shorted as FISK model and TU model). These origin models have attracted wide attention from the community. Recently, we conduct the numerical study on TU model, which shows that the magnetic reconnection as a result of supergranular advection indeed feeds the mass to the nascent solar wind. Based on this, the research about FISK model will further improve our understanding about the origin model as driven by reconnection. On the basis of a developed MHD numerical model, this project will numerically study under FISK model how the material of solar wind are supplyed, and how the waves as excited futher accelerate solar wind, and how parameters of coronal loop influence solar wind. In particular, this project will conduct a comparative study about the different dynamics between FISK model and TU model. The work results are expected to uncloud occurrence and acceleration process of solar wind outflow in FISK model, and to reveal the dominant factor in the origin model as driven by reconnection, and to intensify understanding of solar wind origin mechanism.

太阳风起源问题是空间物理和空间探测的关键科学问题之一。已有模型大多假设太阳风是由光球经色球到日冕沿一恒定流管的稳态流动。基于新的观测结果, Fisk et al., (1999，2003)和Tu et al.,(2005a,b)提出了磁重联驱动的太阳风起源模型（以下分别称为FISK模型和TU模型），并引起广泛关注。最近我们对TU模型进行了数值模拟验证，发现超米粒水平对流引起的磁重联确实能够为初始外流提供所需的物质。在此基础上，对FISK模型的研究将有助于进一步认识磁重联驱动的太阳风起源模型。本项目拟在已建立的MHD数值模式基础上，数值研究FISK模型下太阳风的物质供应，波动激发对太阳风的贡献，和冕环参数对太阳风的影响；特别对比研究FISK模型和TU模型下太阳风起源的动因。预期明晰FISK模型太阳风外流发生和加速过程，揭示磁重联驱动太阳风起源的主导因素，加深对太阳风起源机制的认识。

太阳风是由太阳发出的连续的高温高速等离子体流,是形成日球层的主要介质。自1962年水手2号飞船证实太阳风的存在以来,太阳风的起源，加速和加热一直是尚未解决的基本科学问题。磁重联、波动、湍流被认为对太阳风起源，加速和加热有重要贡献。本研究针对太阳大气的特点，研制了描述太阳大气磁流体重联的2.5维数值模式及描述太阳风湍流的3维可压缩磁流体数值模式。利用太阳大气磁流体重联模式，模拟研究了光球运动驱动的交换重联的物理过程，首次揭示日冕间歇磁场重联激发磁流体力学波动的物理过程。在磁流体数值模拟基础上，利用测试粒子模拟，得到重联区对流电场能够加速电子到200 keV，其中向上运动的高能电子能谱与超热电子能谱一致；表明太阳风中的超热电子可能由太阳大气的磁重联产生。同时，模拟了非线性阿尔分波加速加热太阳风的物理过程，得到日冕底部注入的均一分布的低频阿尔分波在日冕主要分布在远离赤道平面的区域，并且加速等离子体形成高速流；而在赤道平面的附近，阿尔分波耗散，从而形成低速流。利用可压缩磁流体湍流模式，模拟了自由演化的阿尔芬性湍流，首次得到湍流中旋转间断面可由非均匀的阿尔芬速度引起的阿尔芬波的陡化产生；通过提出识别慢波新判据，分析了湍流中慢波的传播演化过程，得到慢波可嵌入在阿尔芬性背景中。