行星际磁场对水星磁层顶位置及位形的控制

The in situ observations of magnetopause dynamics provide a crucial key to understand the interaction of solar wind with planetary magnetosphere. The dynamics of Earth’s magnetopause have been extensively studied; however, so far, the similar research has not been systematically conducted at Mercury due to lack of sufficient observational data for a long time. Mercury’s comparatively weak intrinsic magnetic field, together with the strong solar wind forcing in the inner heliosphere, creates a small and highly dynamic magnetosphere. Therefore, the influence of solar wind and interplanetary magnetic field on the large-scale dynamics of magnetopause are expected to be largely different from each other. Based on the large MESSENGER database, this project will statistically study how the interplanetary magnetic field, especially its radial and southward component, control the position and shape of the Mercury’s magnetopause. In addition, the project will also develop a three-dimensional magnetopause model that parameterized by the interplanetary magnetic field, and reveal the nature of solar wind interaction with Mercury’s weak intrinsic magnetic field. Further, the obtained results will be compared with the present knowledge of the Earth case. New understandings of the different planetary magnetopause dynamics will be gained from this project.

卫星实地探测磁层顶动态变化是理解太阳风与行星相互作用的关键。地球磁层的大量卫星数据促使磁层顶动力学特征被广泛地研究，但水星磁层探测数据的长期缺乏导致该类研究始终没有系统化。水星轨道处强太阳风驱动和弱行星磁场相互作用形成太阳系中尺度最小且动力学特征最活跃的行星磁层空间。因此太阳风与行星际磁场对水星磁层顶大尺度动力学特征的控制机理很可能与地球迥异。本项目拟利用美国新的水星探测计划“信使”号的全部（2011-2015）观测数据，统计分析行星际磁场大小和方向对磁层顶位置及位形的控制影响，重点研究行星际磁场径向分量和南北分量对磁层顶的控制作用，并对水星三维磁层顶模型进行行星际磁场参数化，揭示太阳风与弱磁场行星相互作用规律。进一步与地球空间已有结果比较，以期在太阳风与行星磁场相互作用的普遍规律上获得新的认识。

水星磁层顶动态变化研究对于认识近水星空间环境的演化具有重要的意义。本项目主要是建立“信使”号卫星穿越水星磁层顶和弓激波的数据库，利用该数据库研究行星际磁场（IMF）对水星磁层顶位置及全球性位形控制影响，并与地球相关特征进行比较研究。取得了以下研究进展：（1）建立了完整的穿越水星磁层顶、弓激波及对应的IMF条件事件库；（2）基于事件库建立了IMF参数化的水星三维磁层顶模型，揭示出太阳风与弱磁场行星相互作用规律；（3）区别于地球，发现水星磁层顶全球性尺度显著受控于行星际磁场径向分量，并受行星轨道的周期性调制，而向阳侧磁层顶磁重联的“剥蚀”效应不明显；（4）指出磁尾的强驱动快速脉冲式重联特征，发现了超大磁通量绳的存在证据并提出了相应的形成机理，给出了水星磁层动力学过程的新物理图像。相关研究结果加深了我们对太阳风与行星磁场相互作用过程的理解。