Multi-Scale Electrodynamics of Magnetosphere-Ionosphere Interactions at High Latitudes

Abstract

Recent observations from Polar and Cluster satellites in the high-latitude magnetosphere at geocentric distance from 4 to 7 RE reveal intense, localized electromagnetic structures with characteristic features of shear Alfven waves, which generation in this magnetospheric location cannot be explained within current physical paradigms. In particular, observations show relatively small-scale (10-12 km in projection to 100 km altitude) waves with frequencies ~25-50 mHz. They are observed in the nightside magnetosphere on the boundary between open and closed magnetic field lines, which makes it hard to use for their explanation a classical magnetospheric field resonance theory. The fact that these waves are observed well above 1 RE altitude does not let explain them with a theory of the low-altitude ionopsheric Alfven resonator. Frequencies of these waves, which for the first time have been recovered from the Cluster observation, also do not match characteristic frequencies either of the Alfvenic ionospheric resonator, global magnetospheric field line resonances or substorm onset related Pi2 oscillations. Because these waves are frequently associated with fluxes of accelerated electrons, heavy ions outflow, density cavities, and strongly involve in the redistribution of the ion plasma content between the ionosphere and the magnetosphere, they certainly play a very important role in magnetosphere-ionosphere interactions at high altitudes and mechanisms causing their generation must be investigated. The central questions to study are: 1) What mechanism generates small-scale waves observed in the magnetosphere? and 2) What defines frequency, amplitude and transverse scale-sizes of these waves? To answer these questions we propose to investigate the hypothesis that these waves are generated by nonlinear interactions between large-scale magnetic field-aligned currents and the auroral ionosphere. The central role in these interactions belongs to the ionosphere. This investigation will be curried on by the team of internationally known scientists with excellent research records and high level of expertise in data analysis, numerical simulations and theory. This team will bring together data from the FAST, Polar and Cluster missions, powerful multi-fluid, multi-dimensional MHD simulations and newest theoretical concepts related to this problem. The results from this project will be extremely important for understanding and interpretation of large amount of experimental data from current and future space missions, which makes this project very relevant to the main scientific objective of the International Space Science Institute. The success in this research may lead a significant re-evaluation of the role of ionosphere in the global picture of MI coupling at high latitudes and hence add a significant value to the publicity of research programs performed under the auspices of the International Space Science Institute.