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.
