极光区磁层-电离层电动耦合的三维有限元数值模拟研究

The magnetosphere-ionosphere(MI)electrodynamic coupling in the auroral zone, one of the most importantparts in the energy transfer in the Sun-Earth system, involves the generationand propagation of MHD waves, appearance of field-aligned currents (FACs) and electric field,formation of auroral arcs, as well as the conductance and currents in the ionosphere. These processes are coupled together in multi-scales, especially FACs are closely related to the dispersive Alfven waves in the complicated topology, which has been a great challenge in the modeling of MI interaction. Most previous researchesare either thetheoretical studiesor the numerical modelingbased on a two-dimensionalfinite element model.This project will concentrate on the generation and optimization of unstructured meshes, and the construction of three-dimensional finite element model based on our well-developed two-dimensional model. We aim at studying the dynamical evolution and interaction ofthe field line resonancesof the magnetospheric Alfven wave, as well as the propagation properties of shear Alfven waves from the three-dimensional simulation by the geomagnetic configuration and the plasma density distribution. In particular, the effects of the ionospheric Hall conductivity on the MI coupling and the generation of the aurora will be analyzed, and the comparison with the 2D’s result will be also included. Finally, the project is designed investigate the temporal and spatial evolution of currents and plasma in the auroral region.

极光区磁层-电离层的电动耦合涉及磁流体波的产生和传播、场向电流和电场的出现、极光的形成以及电离层电导率和电流的变化等物理过程，控制着太阳风的能量、动量以及粒子向地球高层大气环境的输运。这些过程往往包含了多空间和时间尺度的耦合，特别是极光现象中的场向电流在很小的色散尺度中产生，所处的磁场位型又变化复杂，在磁层-电离层耦合数值模拟中一直是一个挑战，以往的研究基本上都是理论性工作或者基于二维的数值模拟。本项目将基于申请人已有的二维有限元模型，生成并优化三维不规则网格，构建新的三维磁层-电离层电动耦合有限元模型，模拟极区阿尔芬波（特别是场线共振）的动力学演化和相互作用，分析磁场位形和等离子体密度分布对剪切阿尔芬波传播特征的影响，以及电离层霍尔电导率对磁层-电离层耦合的效应和它在极光产生中的作用，比较与二维情形下的异同，并研究亚暴期间极光区电流和等离子体的时空演化特征。

磁层-电离层的电动耦合是日地能量传输链中的重要一环，在高纬区更是与极光的产生有着密切的关系。基于申请人已有的二维有限元模型，研究了三维不规则网格生成和优化技术，对二维模型进行拓展，建立并完善了基于有限元技术的三维磁层-电离层电动耦合模型，研究了极区阿尔芬波场线共振的动力学演化和相互作用，三维模拟磁场位形和等离子体密度分布对剪切阿尔芬波传播特性的影响，分析了亚暴期间极光区电流和等离子体的时空演化特征、亚暴期间亚暴电流楔中下行场向电流的产生机制、径向太阳风对日侧极光的影响。还进行了三成分冷等离子体中的低频波研究、利用支持向量机预测大磁暴期间Dst指数的变化研究、偶极倾角对弓激波位形的影响研究、行星际磁场对极尖区位形变化的统计研究、建立了新的具有偶极倾斜效应的三维非对称模型、等离子体中的平行传播波和不稳定性研究、亚暴期间太阳风能量和等离子体向磁层的输运、温度各向异性产生的束流不稳定性、地磁暴对中低纬MLT温度的影响等。