Title: Statistical study on propagation characteristics of Omega signals (VLF) in magnetosphere detected by the Akebono satellite,
Abstract: This paper shows a statistical analysis of 10.2 kHz Omega broadcasts of an
artificial signal broadcast from ground stations, propagated in the
plasmasphere, and detected using an automatic detection method we developed. We
study the propagation patterns of the Omega signals to understand the
propagation characteristics that are strongly affected by plasmaspheric
electron density and the ambient magnetic field. We show the unique propagation
patterns of the Omega 10.2 kHz signal when it was broadcast from two
high-middle-latitude stations. We use about eight years of data captured by the
Poynting flux analyzer subsystem on board the Akebono satellite from October
1989 to September 1997. We demonstrate that the signals broadcast from almost
the same latitude (in geomagnetic coordinates) propagated differently depending
on the geographic latitude. We also study propagation characteristics as a
function of local time, season, and solar activity. The Omega signal tended to
propagate farther on the nightside than on the dayside and was more widely
distributed during winter than during summer. When solar activity was at
maximum, the Omega signal propagated at a lower intensity level. In contrast,
when solar activity was at minimum, the Omega signal propagated at a higher
intensity and farther from the transmitter station.