行星际日冕物质抛射的磁流体数值模式正演和白光射电遥测反演的联合研究

Observations in white light, interplanetary scintillation (IPS), and Faraday rotation are the main remote-sensing means for monitoring the inner heliosphere. Using white light imaging, interplanetary coronal mass ejections (CMEs) can be continuously tracked. Remote sensing signatures as a result of line-of-sight integration involve Thomson scattering effect for white light imaging and thin-phase-screen approximation for IPS signatures. Inversion and interpretation of remote sensing observation data suffer from large uncertainties, particularly at large elongations from the Sun. Kinematic CME models are needed to interpret brightness patterns of CMEs imaged by the STEREO/HIs, and low-frequency IPS signatures recorded by radio telescope array. In this proposal, we plan to use forward magnetohydrodynamic (MHD) modelling of the inner heliosphere in generating synthetic observations, analyze the observation data of STEREO/HI and IPS to infer local physical parameters, and compare modelling results with realistic observation events. We aim to uncover the kinematics and dynamics of interplanetary CMEs, establish the causal correspondence between CME dynamics and remotely observable signatures, understand remote-sensing capabilities of white-light and low-frequency radio techniques, and propose the feasible strategies and methods for space weather predicting. Our numerical MHD model is expected to be validated by observation data. Using our MHD model, we intend to predict the coordinated imaging observations of CMEs in white-light and radio, predict the white-light patterns of CMEs imaged by future satellites from the Lagrangian point L4/L5 and the solar polar orbit.

白光成像、行星际闪烁(IPS)、法拉第旋转是内日球层的主要遥感探测手段。白光成像能连续跟踪日冕物质抛射(CME)的传播和演化。遥感信号涉及视线方向的积分效应，具体是白光的汤姆逊散射效应和IPS的薄相屏近似等。遥感信号的反演和推断存在不确定性，需要CME运动学模型才能解读STEREO/HI所拍摄的CME白光影像和低频射电望远镜所记录的闪烁信号。本项目采用内日球层MHD数值模式正演和白光射电遥感观测反演，将模型计算结果与典型观测事件比对，研究行星际CME运动学和动力学，建立行星际CME动力学和白光射电观测表现的对应关系，加深理解遥感成像技术的探测能力，为空间天气预报发展策略和方法，利用观测数据检验MHD数值模式的正确性。基于该正演数值模式，预测行星际白光和射电的联合成像对CME的观测结果，预测将来部署在L4/L5点和太阳极轨的科学卫星所能拍摄的CME白光影像。

在面上基金的资助下，本项目综合利用三维磁流体力学数值模拟、白光汤姆逊散射理论、深空卫星轨道动力学，在日冕和行星际的白光辐射亮度、日球层卫星探测计划的科学论证这两方面取得如下重要的科学进展：.（1）追踪日冕物质抛射CME在行星际空间的完整传播过程，自洽合成CME驱动鞘区的白光辐射亮度，阐明CME白光影像形态显著依赖于卫星观测视角，解释白光日球仪STEREO/HI在1 AU漂移轨道处所拍摄的各种CME影像，从而为未来空间卫星计划搭载白光日球仪提供“科学目标定义与载荷配置方案”的科学论证（Xiong et al, ApJ 2013）。.（2）分析内日球层背景太阳风的白光辐射本底，正演行星际共转流相互作用区CIR的白光影像。论证未来太阳极轨卫星搭载的广角白光成像仪能够分辨：(i) CIR在经度方向的大尺度螺旋型结构特征；(ii) 揭示CIR在日冕源区的初发过程及其在行星际空间的陡化发展（Xiong et al, ApJ 2017）。.（3）分析内日球层CME扰动的白光辐射亮度，发现CME鞘区的辐射形态随观测视角的变化是归因于背景太阳风中高速流和低速流的三维分布，揭示脱离黄道面的白光全景成像能够分辨CME经度结构细节。论证未来太阳极轨视角的白光成像优势：(i) 追踪CME在日地空间的传播过程；(ii) 确定CME在经度的范围和在黄道面内的传播速度（Xiong et al, ApJ 2018）。..项目执行达到预期目标，共计发表论文9篇：第一作者论文5篇（其中3篇ApJ），合作论文4篇。上述3篇ApJ系列论文被审稿人高度评价为：“a useful landmark in the ongoing buildup to an out-of-ecliptic mission”、“interesting both from the scientific and mission-support perspectives”、“very up-to-date and of special interest with regard to the future Parker Solar Probe and Solar Orbiter missions”。