SuperDARN studies of magnetospheric ULF waves and boundaries

点击翻译按钮获取中文摘要

Ultra-low-frequency (ULF) waves propagating within the magnetic field and hot ionized gas (plasma) of interplanetary and near-Earth space constitute one of the most important means by which energy is exchanged within and between the outflowing stream of solar plasma, the solar wind, and the Earth's magnetic field environment, the magnetosphere. Magnetospheric ULF waves are known to be associated with important phenomena such as auroral arcs, substorms, radiation belt energization, and magnetic reconnection. Yet the source mechanism driving much of the discrete ULF wave activity in the magnetosphere remains unconfirmed and is currently a topic of considerable debate. In particular there is a class of ULF wave in the magnetosphere called the field line resonance (FLR) where the Earth's magnetic field lines resonate at their characteristic frequency like a standing wave on a string. Remarkably these FLRs are often observed at very discrete and reproducible frequencies and the reason for this is not understood. An emerging idea is that discrete oscillations in the solar wind directly drive ULF waves in the magnetosphere including the discrete FLRs. The first objective of this proposal is to determine what proportion of magnetospheric ULF waves are driven directly by a solar wind wave source. The second objective is to investigate how magnetospheric ULF waves evolve in time and space from the magnetopause boundary to the inner magnetosphere and down to the ionosphere. To achieve these objectives a database of magnetospheric ULF wave events will be compiled and analyzed using the Super Dual Auroral Radar Network (SuperDARN), an international network of high frequency radars which measures high latitude ionospheric plasma flows with high time and spatial resolution. SuperDARN convection maps will also be used to develop a new ionospheric convection gradient technique to study magnetospheric boundaries and dynamics.