热各向异性空间等离子体中的离子尺度以上的磁洞的本质的研究

Magnetic holes are common structures appearing in space plasma. They play an important role in particle transportation and transformation of magnetic energy. They are also a typical coherent feature in turbulence. However, there is still a debate on the nature of magnetic holes. As to magnetic holes above ion-scales, there are two mainstream explanations: mirror-mode instability regarded as non-propagating, and obliquely-propagating slow magnetosonic wave. The debate is going on, large owing to the common feature: anti-correlation between magnetic and thermal pressure, which fails to distinguish the two modes. Data obtained from one single spacecraft can hardly tell whether a feature is propagating, needless to say some kind of characteristic velocity. Therefore, a method must be sought to distinguish the modes, which should be convenient to work with single-spacecraft data. ..This project aims at establishing such a method. We intend to start with magnetohydrodynamics with thermal anisotropy described by double-polytropical equations. We will solve for the modes and compare them for common features and distinctions. With such knowledge, we will analyse relationships between physical quantities in observed magnetic holes, and establish a model to simulate the observed features of magnetic holes. This model will better clarify the nature of magnetic holes above ion-scales. Moreover, we will also to establish numerical models where magnetic holes are formed self-consistently in space turbulence, which will exhibit the relationship between magnetic holes and the both modes, as well as effects of magnetic holes on turbulence spectra.

磁洞是空间等离子体中常见的结构，对于粒子传输和磁能转换有重要作用。磁洞也反映了湍流中一种典型的相干特征。然而，就磁洞的本质，目前还存在争论。就离子以上尺度的磁洞的成因而言，主要观点有二：不传播的磁镜模不稳定性，及倾斜传播的慢磁声波。该争论尚无定论，是因为这两者有磁压和热压的可压缩的相似性，即均表现为反相关，容易引起混淆。使用单点卫星探测数据，也很难诊断磁洞是否传播，遑论测定其传播速度。因而，必须寻求方法，以体现两个模的区别，而这种区别又应方便单卫星观测的利用。.本项目的目标，即是建立这种方法。本项目计划从双多方热各向异性的磁流体力学理论切入，全面探讨斜传慢模与磁镜模的异同，进而有针对性地分析磁洞观测中各参数的关联，并在此基础上基于理论结果建模，以仿真磁洞的观测特征，从而阐明离子以上尺度磁洞的本质；本项目还将构建湍流中自洽产生磁洞的数值模型，以探讨磁洞与两个模的关系，及对湍流功率谱的影响。

太阳风是日球层物质的首要存在和流动形式。由于太阳活动性的存在，及太阳风本身的超雷诺数流动，太阳风体现出明显的时空变化性，对这种变化性的研究，是推动空间科学发展、驱动空间探测技术进步的重要途径。本项目由磁洞这一空间不均匀性出发，探究对时空变化的观测分析手段与物理本质，落实在两个主要方向上：（一）多卫星星座对时空变化的观测数据分析方法；（二）分析到的扰动的物理本质判读，尤其体现在压缩阿尔文性脉动的日面起源方面。..多卫星星座观测数据分析方法意在以磁洞等空间变化现象为载体，开展时空分离的空间就地探测数据分析方法。在此方面，本项目研究给出了多星星座波矢空间混叠效应的计算方法，在保证结果准确性的前提下，利用混叠效应的本质减少了计算量负担。研究成果定量分析了多星星座对湍流功率谱探测中波矢空间的指标，为多星星座探测空间天气过程或时空物理变化本质提供定量约束与辅助规划工具。..为了明晰典型的空间阿尔文性陡变现象的来源，本项目也构建了太阳大气重联间断性引发阿尔文性脉动的数值模型，提出了太阳大气重联触发日地空间阿尔文性脉动的初始注入阶段机理。本模型的间断性重联由对应日面对流模式的导向场注入引发，在重联区形成阿尔文性脉动，从而对近年帕克太阳探针 (PSP) 等给出的新的观测事实给出诠释。..本项目的研究结果将作为打通太阳大气过程——行星际空间——观测计划——数据分析链条的有力结点，建立的方法与模型除空间物理学相关领域的分析研究外，也能够在服务于空间物理学或空间天气的探测项目论证、探测计划设计等方面提供有力的协作工具。