利用多行星观测数据研究ICME携带的磁场湍流的径向演化

The magnetic turbulence, which is accompanied by the variations of the electromagnetic field and the plasma properties, is a common and complicated phenomenon in the planetary and interplanetary space environment. It plays an important role in the energy transfer and conversion. Thus, the magnetic turbulence is always a hot and difficult topic in space physics research. The magnetic turbulence carried by the interplanetary coronal mass ejection (ICME) is an important topic in the space weather research, because of its strong modulation of the magnetic field and plasma properties in the boundary of the ICME. However, it is difficult to study an ICME from multi-position along one radial direction owing to its high propagating speed. Until now, the study of the magnetic turbulence carried by the ICME is mostly constrained at 1 AU and the radial evolution is rarely concerned. Recently, high quality observation data obtained by many planetary explorations from NASA and ESA provides a great opportunity to study the radial evolution of the magnetic turbulence carried by the ICME. This project, utilizing the joint observations from the orbit of Mercury, Venus, Earth, and Mars, focuses on studying the magnetic turbulence carried by the ICME at different distances along a rough radial direction to get the radial evolution law of the power spectral density of magnetic turbulence. Finally, a proper function will be addressed to describe the radial evolution of the power spectral density of the magnetic turbulence quantitatively. This project will help us to deepen the understand of the planetary space weather effectiveness and provide scientific basis to the relevant scientific goal setting of Chinese Mars exploration.

磁场湍流是行星际和行星空间环境中常见而又复杂的扰动现象，其伴随着电磁场与等离子体状态的变化，并能引起能量的转移与转化，因而一直是空间物理研究的热点与难点。行星际日冕物质抛射（ICME）携带磁场湍流并在传播过程中发生演化，对ICME边界处磁场与等离子体状态有显著调制作用，也成为空间天气研究关注的重要问题。由于ICME的快速传播，以往很难对同一ICME沿（近似）同一径向多点观测。目前对ICME所携带的磁场湍流的研究多集中在1AU处，较少涉及传播演化问题。近些年欧美多次行星探测获得了高质量观测数据，提供了很好的研究契机。本项目将利用水、金、地、火四颗行星轨道处的联合观测，分析不同轨道处ICME所携带的磁场湍流的特征，归纳功率谱密度随径向距离的变化，并定量描述其径向演化规律。预期研究结果还将加深对行星空间天气效应的理解，并为我国火星探测的相关科学目标的设定提供科学依据。

行星际日冕物质抛射(ICME)是影响行星空间环境的重要因素。CME传播速度足够大时常在其前方驱动产生一个激波。从其太阳源区触发开始，CME就携带丰富的湍流，CME驱动激波的下游更是湍流最丰富的区域。激波上游磁场湍流主要影响激波对粒子的加速，而激波下游磁场湍流主要影响ICME与行星空间的相互作用以及对银河系宇宙射线的调制。ICME本身及其携带的磁场湍流在其传播过程中都是时刻演化的。 本项目主要基于多点观测数据，获得了以下三方面的主要研究进展：（1）构建ICME数据库，获得ICME驱动激波上下游的磁场湍流功率谱密度的径向演化规律。激波上游的磁场扰动功率谱密度在惯性尺度的径向演化依赖于频率，频率越高径向衰减越快，这也相应的导致激波上游惯性尺度的磁场扰动功率谱密度随径向距离增加而变陡，从0.3AU到1.08AU其谱指数从约-1.3降低到约-1.8；而激波下游的磁场扰动功率谱密度在惯性尺度的径向演化基本不依赖于频率，从而使得其谱指数基本不变约为-5/3。（2）厘定ICME是有史以来最强火星X射线辐射的驱动源，解决了XMM-Newton观测遗留10多年的科学问题。（3）将激波跃变关系扩展应用到太阳遥测数据，开发出定量诊断太阳大气激波参数的新方法。

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