Auroral arcs are the result of localized particle acceleration following either an electrostatic process or a more dynamic wave-particle interaction at a few thousand kilometers above the ionosphere. Discrete arcs regularly display small- and meso-scale distortions that can appear suddenly and move with speeds that are not related to plasma speeds in the ionosphere but rather represent properties of the acceleration processes in the magnetosphere. The temporal and spatial structure of each small-scale structure is thus evidence for its distinct dynamic role in the interaction between the hot magnetospheric and the cold, dense ionospheric plasmas. The science objective of the international ISSI team is to investigate:
- the origin of discrete, kilometer-size auroral structures, and
- their importance as markers of magnetospheric processes in the Sun-Earth-System.
The team combines the experience from many space missions and seeks to combine spacecraft data with ground-based observations and the theoretical investigations in order to achieve a better understanding of the role of small- and meso-scale auroral features. Specifically the team will investigate which processes control the sudden appearance, the size, and the motion of these auroral features. Furthermore, the team seeks to obtain a better understanding of the influence of such structures on the ionosphere and their role and effect on the global magnetosphere-ionosphere system. The availability of optical auroral data from space missions (Polar, IMAGE, REIMEI) and the extended THEMIS ground-based network and additional spacecraft plasma and field measurements make the proposed project a very timely investigation. The anticipated result will be a review paper summarizing the event studies and advances that were achieved by the team and pointing to future directions to enhance the knowledge about the origin and function of small-scale auroral structures.