Experimental Studies of Auroral Arc Generators 1

This is the final report of a three-year, Laboratory-Directed Research and Development (LJXD) project at the Los Alamos National Laboratory (LANL). An all-sky video camera system was deployed in Eagle, Alaska at the foot of the magnetic field line that threads geosynchronous satellite 1989-046 as part of a campaign to study correlations of ground-based auroral activity with satellite-based plasma and energetic particle measurements. The overall intent of the project was to study magnetosphere-ionosphere coupling as it relates to the aurora, and, in particular, to look for signatures that may help to identify various auroral generator mechanism(s). During this study, our efforts were primarily directed towards identifying the generator mechanism(s) for pulsating aurora. Our data, though not conclusive, are found to support theories that propose a cyclotron resonance mechanism for the generation of auroral pulsations. Background and Research Objectives The auroral ionosphere and its corresponding magnetospheric domains have been intensively studied by both ground-based and in situ-based instrumentation for over 30 years. Despite the vast amount of knowledge that has been gained from these studies, the basic mechanisms that govern the generation of most auroral forms (in particular, discrete auroral arcs and auroral pulsations) have yet to be conclusively identified. Much of the difficulty in identifying these mechanisms relates to the fact that the generation regions and particle acceleration regions for a specific auroral form are usually far removed from, and in radically different plasma environments than, the region where precipitating auroral particles manifest themselves as visible auroral activity. This system complexity effectively precludes the possibility of using single-point measurements for the positive identification of auroral generator mechanisms. *Principal Investigator, E-mail: dsuszcynsky@lanl.gov Over the years, there have been numerous attempts to make magnetically conjugate multi-point, multi-phenomenology observations of auroral activity in order to identify and study auroral generator mechanisms. The most promising studies have involved groundbased auroral imagery stations at locations magnetically conjugate to satellite-based plasma, particle, and magnetic/electric field instrumentation.'-' However, the results of most of these studies have been limited by brief or marginally conjugate satellitelground station alignments and/or short-term ground campaigns. In this paper, we describe our efforts to field and operate a system that provides continuous, long-term monitoring of auroral activity at a ground station that is magnetically connected to a geosynchronous satellite. Our intent was to collect long-timescale data sets that can be used to address, both on a per case basis and on a statistical basis, the mapping of magnetospheric domains into their auroral counterparts, the identification of various auroral generator mechanisms, and/or the validity of existing theories of auroral generator mechanisms. Geosynchronous orbit is optimal for this type of study for two reasons: (1) since a geosynchronous satellite corotates with the earth, its magnetic footprint on the earth remains fixed, allowing for a continuous long-term monitoring of a magnetic field line with fiied, ground-based equipment, and (2) geosynchronous orbit samples several key regions of the magnetosphere that are believed to be source regions for various auroral forms: the ion and electron plasma sheets, the trough, and the plasmasphere. Importance to LANL's Science and Technology Base and National R&D Needs This project was important to LANL's science and technology base in that it utilized and further developed LANL's expertise and capabilities in the areas of ionospheric and magnetospheric science. Such competencies are useful in advancing basic scientific knowledge and enhancing the laboratory's reputation of excellence in carrying out quality scientific studies. In particular, it is important to maintain these competencies for programmatic purposes, in this case, to maintain our ability to measure, model and understand optical transient events in the ionosphere and magnetosphere related to atmospheridionospheric nuclear detonations. Scientific Approach and Accomplishments The campaign described in this report ran from October 1,1994 to mid-April, 1995. The experimental setup consisted of a ground-based all-sky video camera that was fielded in Eagle, Alaska at the foot of the magnetic field line that threads geosynchronous satellite 1989-046 (Figure 1). The all-sky video camera was fielded and maintained by T. A.