A Proposal for the Measurement and Analysis of Extremely Low Frequency (ELF) Waves at South Pole Station

点击翻译按钮获取中文摘要

This project will detect and record magnetic field fluctuations in the Extremely Low Frequency (ELF) range at South Pole Station. The range of frequencies being measured (1 to 350 Hz) encompasses interesting and important phenomena related to magnetosphere-ionosphere coupling. The primary objective is to characterize auroral ion cyclotron waves, which, according to theory, modulate precipitating electron fluxes, causing the flickering in auroral luminosity emissions. Substantial evidence now exists in support of this theory, although the excitation mechanism responsible for the ion cyclotron waves is somewhat uncertain. Perhaps the most well-developed theory suggests that the waves result from an electron beam instability. In any case, the frequency of the flickering or, equivalently, the frequency of the ground-based observations of ion cyclotron waves can be used to infer the altitude of the excitation mechanism, since the wave frequency depends on the strength of the known background magnetic field. As such, the information that will be acquired as part of this project can be used to test models of auroral acceleration mechanisms. The second objective of this project is to study dispersive ELF waves, a type of wave that has been reported in the literature only a few times, but one that may provide important information regarding substorm onset or, perhaps, boundaries of open and closed magnetic fields. A first step in the project is to identify the wave mode and to determine the location and geomagnetic conditions under which these waves are observed. Ultimately the most important parameter to be quantified is energy transfer, which occurs via Poynting fluxes and particle energy. A significant fraction of the particle energy flux is associated with auroral phenomena, so to a great extent our knowledge of magnetosphere-ionosphere coupling depends on how well we understand auroral processes.