ELF Sferic Occurrences in the Antarctic during a Solar Proton Event: Case Study of Occurrences at Byrd Station during the Event of 9 June 1968

摘要

Electromagnetic waves with frequencies above the extremely-low-frequency range (ELF; frequencies in the range 5 Hz-3) are susceptible to a variety of solar proton event (SPE) effects when propagating through a polar region in the earth-ionosphere waveguide. These effects appear to become less severe as the frequency of the waves becomes smaller and approaches the ELF range. Although measurements have been lacking, it would be expected that ELF wave propagation through the polar regions would be comparatively stable. To investigate polar ELF wave propagation during an SPE, we have carried out a series of measurements of the properties of ELF sferics (75 Hz) at a polar location (Byrd Station, Antarctica) during a moderately-large SPE. These measurements suggest that an SPE can significantly alter the characteristics of ELF signals propagating through the polar regions: during the first 24 hours of the SPE there was a reduction of about 50% in the median amplitudes of the sferics, compared with their amplitudes before the SPE, and there were substantial changes in their rates of occurrence.