Narrow-band extremely low frequency (ELF) wave phenomena observed at South Pole Station

Extremely low frequency (ELF) magnetic pulsations which show a whistler-like spectral structure have been measured at South Pole Station. An initial survey of the first 70 days of data revealed narrow-band ELF pulsations with slowly varying frequency over time. The narrow-band (a few Hz) signatures maintain their bandwidth as their frequencies decrease from 110 to 50 Hz (and their second harmonics) over the course of 40-90 s. Although the narrow-band ELF waves have a signature somewhat similar to very low frequency (VLF) whistlers, their duration and frequency range are much different from those of whistlers; they also show an unusual characteristic where their frequency often increases before it decreases. These events show a peak in their magnetic local time (MLT) occurrence distribution near the pre-midnight region, a result that contrasts sharply with the only three previously published studies of these waves. Two possibilities of generation mechanism are discussed.