A new natural radio emission observed at South Pole Station

摘要

Continuous waveform data taken at South Pole Station in 2011–2012 within a few hours of magnetic midnight revealed 12 observations of a new natural radio emission. The waves had frequencies ranging from 1320 to 2160 kHz, bandwidths ranging from 94 to 272 kHz, and durations ranging from 16 to 355 s. Spectral analysis of the waveform data revealed that the emission has a complex combination of at least three kinds of fine structures: broad, banded structures; short-lived, narrowband structures; and striated features that occur predominantly near the lower frequency boundary of the emission. For model auroral electron distributions, positive growth rates for the cyclotron maser instability occurred near the electron cyclotron frequency (f_(ce)), which is inconsistent with the observed wave frequencies. On the other hand, Langmuir wave growth could be excited at frequencies consistent with observations. Spatial Langmuir wave growth is more favorable for electron beam energies of hundreds of eV than for those at higher energies.