17:15 〜 17:30
[PEM04-17] Polarization and occurrence statistics of VLF/ELF chorus waves at sub-auroral latitudes at Athabasca, Canada.
キーワード：VLF, Chorus Waves, Polarization analysis, Ionospheric exit point, Sub-auroral latitudes
Chorus waves are whistler-mode emissions in the very low frequency (VLF) range that are one of the most intense and common natural emissions. They are generated in the inner magnetosphere at the geomagnetic equator and follow the geomagnetic field lines into the ionosphere and the ground. They are believed to be one of the major contributions to the acceleration and scattering of radiation belt particles (e.g., Inan et al., 1982; Omura et al., 2007). Consequently we are interested in the spatial and temporal motion of the acceleration region of radiation belt electrons, which might be directly linked to the motion of the Ionospheric footprints of VLF/ELF waves. For a period of 9 days, from February 17 to 25, 2012, the VLF-CHAIN campaign observed VLF/ELF emissions at sub-auroral latitudes using two loop antennas at Athabasca (MLAT=61.31, L=4.3) and Fort Vermillion (MLAT=64.51, L=5.4), Canada. Several interesting features of chorus emissions have been observed such as quasi-periodic emissions, falling-tone and rising-tone chorus, as well as Bursty-Patch emissions. We have applied polarization and spectral analysis to make the first comprehensive study of the physical properties of VLF/ELF chorus waves at sub-auroral latitudes. Combining these analyses with a triangulation method we have also identified the location and motion of the Ionospheric exit points of these various types of chorus waves. Furthermore, after September 24, 2012, continuous measurements of VLF/ELF waves with a sampling rate of 100 kHz have been made at Athabasca. Based on this data we show in this presentation the preliminary results of a one-year statistical analysis of frequency and occurrence rate of VLF/ELF chorus waves at sub-auroral latitudes.