Role of Collisionless Reconnection Mechanisms in Solar Flares and Coronal Mass Ejections (CMEs)

磁重联被广泛认为在太阳耀斑和日冕物质抛射（CME）的大多数理论模型中起着重要作用。这些模型通常基于电阻磁流体动力学（MHD）方程，其中拓扑变化和能量耗散的动力学完全由等离子体电阻率控制。霍尔MHD模型可以描述日冕中一些最重要的无碰撞效应。电阻性MHD和霍尔MHD模型之间最重要的区别在于它们对欧姆定律的处理。而电阻MHD模型采用标准电阻欧姆定律，霍尔MHD模型采用广义欧姆定律，其中不仅包括等离子体电阻率，但也包括额外的条款，如霍尔电流。霍尔磁流体效应可能解决一些悬而未决的科学问题，这些太阳耀斑和日冕物质抛射的特点不仅是快速增长，但也由“冲动”，即突然增加的时间导数的增长率（所谓的“触发”问题）。提出了一个基于Hall MHD模型的无碰撞重联的理论研究方案，采用解析方法以及采用自适应网格加密（AMR）的大规模并行代码。建议的任务包括彻底调查的触发问题，结构和涉及的重联网站（S），脚点剪切的影响，多个拱廊，和完全自洽霍尔磁流体动力学模拟的磁通绳模型。这一研究方案的成果预计将加强和补充日冕重联理论的现有框架，包括重要的无碰撞过程，这些过程已被证明在实验室和其他空间等离子体研究中具有价值，拟议的努力将结合从高中到研究生学习的各级教学和研究。它包括：（1）参加新罕布什尔州大学的一个名为“SMART项目”的暑期研究所（二）与其他机构合办“研究与探索”暑期实习试验计划，让大三及大四的本科生参与;（3）培养一名研究生并指导一名初级研究教员。这项工作还将促进与广大空间等离子体和实验室物理学家的跨学科互动。

Magnetic reconnection is widely believed to play a significant role in most theoretical models of solar flares and coronal mass ejections (CMEs). These models are generally based on resistive magnetohydrodynamic (MHD) equations, where the dynamics of topological change and energy dissipation are controlled entirely by the plasma resistivity. The Hall MHD model can describe some of the most significant collisionless effects for the solar corona. The most important difference between resistive MHD and Hall MHD models lies in their treatment of Ohm's law. Whereas the resistive MHD model employs the standard resistive Ohm's law, the Hall MHD model employs the generalized Ohm's law, which includes not only the plasma resistivity but also additional terms such as the Hall current. It is proposed that Hall MHD effects can potentially resolve some outstanding science issues pertaining to those solar flares and CMEs that are characterized not only by fast growth, but also by "impulsiveness," that is, a sudden increase in the time-derivative of the growth rate (the so-called "trigger" problem). A theoretical research program is proposed on collisionless reconnection based on the Hall MHD model, using analytical methods as well as massively parallel codes that employ adaptive mesh refinement (AMR). The tasks proposed include a thorough investigation of the trigger problem, the structure of and the flows involved in the reconnection site(s), the effects of foot point shear on multiple arcades, and fully self-consistent Hall MHD simulations of flux rope models. The results of this research program are expected to enhance and complement the existing framework of coronal reconnection theory by including important collisionless processes that have already proved to be valuable in studies of laboratory and other space plasmas.The proposed effort integrates teaching and research at all levels, from high school to graduate studies. It includes: (1) participation in a summer institute at the University of New Hampshire called "Project SMART" (Science and Mathematics Achievement through Research Training), which provides exciting research experiences for local high school students; (2) co-sponsorship of a pilot Summer Internship in the "Research And Discover" (RAD) program for undergraduates in their junior and senior years; and (3) training a graduate student and mentoring a junior research faculty member. This work will also promote interdisciplinary interactions with a broad community of space plasma and laboratory physicists.