由X射线成像图到三维磁层顶位形结构的反演研究

At present, the observational analysis of the position and configuration of the magnetosphere mainly relies on in-situ detection of satellites, which fails to provide real-time magnetopause on the large scale. In this context, a space science mission has been proposed by scientists from China and Europe: the Solar wind – Magnetosphere – Ionosphere Link Explorer (i.e., the SMILE mission). SMILE will probably provide images of the magnetosphere for the first time and lay the observational basis for explorations of solar wind-magnetosphere coupling processes. However, what the satellite will observe are two dimensional images, and how to get the three dimensional magnetopause from the images is a fundamental problem remain to be solved, which directly affects the scientific goals and outputs of this mission. Based on the images obtained by performing MHD simulation, this effort will study the inversion from two dimentional images to three dimentional magnetopause positions, and then establish a reliable method to do this inversion. Moreover, systematic simulations under different solar wind conditions will be performed to verify the universality of this method. Then a typical storm event will be simulated and analyzed using the proposed method, in order to reveal the dynamic evlutions of large scale magnetospheric configurations. Through all the above works, we aim at presenting a new method to provide real time magnetopause positions on the large scale.

目前对磁层顶位形的观测研究主要依赖于就地卫星的单点探测，很难实时给出三维的磁层顶位形结构。在此背景下，中欧联合空间科学卫星任务—太阳风-磁层相互作用全景成像卫星（SMILE）应运而生。该计划有望首次给出大尺度磁层顶的实时图像，为人类探索太阳风-磁层耦合基本过程提供观测数据。然而卫星观测数据是二维X射线成像图，如何由成像反演得到三维磁层顶位形是一个尚待解决的基本问题，直接关乎卫星科学目标的实现和科学产出的获得。本项目将以全球MHD模拟得到的二维X射线成像图为出发点，探索并研究三维磁层顶位形结构的反演过程，以建立一个由X射线成像图得到磁层顶三维位形的可靠方法。并且通过系统模拟不同太阳风条件下的算例，检验上述方法在太阳风参数可变范围内的普适性。然后针对典型磁暴事件进行全程模拟，展现大尺度磁层结构的动态演化。从而提供一个可以实时给出大尺度磁层顶位形的新方法。

针对单点就地探测卫星在认识大尺度磁层空间结构方面的局限性，中欧联合空间科学卫星任务—太阳风-磁层相互作用全景成像卫星（SMILE）应运而生。该计划有望首次给出大尺度磁层顶的实时图像，为人类探索太阳风-磁层耦合基本过程提供观测数据。本项目为SMILE发射前的预先研究内容，主要考察由二维X射线成像数据，如何反演得到具有明确物理意义的三维磁层顶位形。基于全球磁流体力学（MHD）模拟程序，我们提出了两种反演方法：切向拟合法和边界拟合法，并在不同太阳风条件及不同轨道位置情况下考察其适用性，给出了适用范围。在此基础上，总结了磁层X射线成像反演的“兵器库”。针对日冕物质抛射事件（CME），采用XMM-Newton卫星数据给出了磁层X射线辐射的基本特性；呈现出了磁层大尺度结构在太阳风扰动作用下的动态演化。该项目的研究结果给出了磁层X射线分布的基本特性和演化规律，开发的反演算法可以直接应用于SMILE科学应用系统，以生成X射线成像仪的高级数据，为保障SMILE的科学产出打下坚实基础。