磁尾重联对不同行星际磁场条件的响应

Magnetic reconnection is the most significant dynamic process to rapidly convert the magnetic energy to the kinetic and thermal energy of the plasma. In the Earth’s magnetotail, the reconnection predominantly occurs in the near-Earth and distant-tail regions. The magnetospheric activities, including both substorm and storm, highly depend on the tail reconnection. Previous studies show that the near-Earth reconnection is bursty reconnection, while the far-tail reconnection is probably steady reconnection. The near-Earth reconnection is closely related with the condition of the interplanetary magnetic field (IMF). Both the location and the strength of the near-Earth reconnection could be different under the different IMF conditions, furthermore, to affect the geomagnetic activities. Till now, we lack the direct and systemetic observations of the response of the tail reconnection to the different IMF conditions. With joint observations of ACE, Wind, MMS, TC-1, Cluster and Geotail satellite observations, we statistically investigate the reconnection in the different tail regions and its response to the IMF conditions. This is significant for us to understand the triggering mechanisms of the magnetic reconnection and the mode of the solar wind-magnetosphere coupling.

磁场重联是最重要的由磁能向等离子体能量（包括热能和动能）快速转化的能量转化方式，是太阳风-磁层耦合系统最重要的动力学过程。在地球磁尾重联主要发生在近地磁尾和远磁尾两个区域。以往的研究表明近地磁尾重联主要是爆发的。但远磁尾的重联有可能是稳态的。近地磁尾重联与南向行星际条件密切相关。其次，在不同行星际条件下近地磁尾重联的位置和强度都有明显不同，从而导致地磁活动明显不同。迄今为止，磁尾重联对不同行星际的响应尤其是北向行星际条件缺乏直接和系统的观测研究。本课题拟利用多颗卫星包括ACE,Wind, MMS，Geotail，Cluster，双星和THEMIS卫星长期的观测，系统分析磁尾（10RE-200RE）不同区域的重联信号,了解近地磁尾和远磁尾重联对不同行星际条件的响应过程。这对我们了解磁重联的触发机制和太阳风-磁层耦合模式具有重要的意义。

本课题利用THEMIS, MMS的数据对磁尾重联和高速流系统分析和研究进行了细致的研究。主要研究目标是了解磁尾重联和高速流的性质。重联喷流是磁尾最重要的现象之一。目前我们在喷流现象上已经取得了很多观测结果，为未来建立喷流湍动的物理模型奠定了基础。本课题主要研究内容包括： 太阳风的统计特性，磁尾高速流的湍动性质和涡场观测特性，磁尾高速流内嵌入的电流片特性等。观测结果确认了BBF期间涡场的存在和增强。特别需要指出的是BBF vorticity的增强与高能离子通量增强形成的手指结构(figure-like structure)密切相关。我们的研究也显示BBF 中等离子体涡向小尺度串级(eddy cascade)过程中可以激发动力学阿尔芬波(kinetic Alfvénic wave, KAW)。因此，BBF是涡(eddy)和KAW共存并且相互作用的复杂湍动现象。