Longitudinal Extent of Magnetospheric ELF/VLF Waves using Multipoint PWING Ground Stations at Subauroral Latitudes

• Published in: Journal of geophysical research. Space physics 2019-12, Vol.124 (12), p.9881-9892
• Main Authors: Takeshita, Yuhei, Shiokawa, Kazuo, Ozaki, Mitsunori, Manninen, Jyrki, Oyama, Shin‐Ichiro, Connors, Martin, Baishev, Dmitry, Kurkin, Vladimir, Oinats, Alexey
• Format: Article
• Language: English
• Subjects: Acceleration; Antennas; Auroral electrojet; Auroral electrojets; chorus wave; Electrojets; Electrons; ELF/VLF wave; Extremely low frequencies; Geomagnetic storms; Geomagnetism; Ground stations; Ground-based observation; ground‐based network observations; Ionosphere; longitudinal extent; Loop antennas; Magnetic fields; Magnetic flux; Magnetic storms; magnetosphere; Magnetospheres; Particle interactions; plasma wave; Plasma waves; Radiation; Radiation belts; Relativism; Relativistic effects; Statistical analysis; Time series; Very Low Frequencies; Waves
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2019JA026810

Magnetospheric extremely low frequency/very low frequency (ELF/VLF) waves are plasma waves emitted from high‐energy electrons in the magnetosphere. These waves have received much attention, as they contribute to the acceleration and loss of relativistic electrons in the radiation belts through wave‐particle interactions. The longitudinal extent of ELF/VLF waves has not been well‐understood, although the extent is important in quantitative evaluation of relativistic electron variations. In this study, we analyzed data from continuous ground‐based simultaneous observations of ELF/VLF waves over a 2‐month period in November and December of 2017, using six loop antennas located at roughly equal intervals around the north geomagnetic pole at ∼60° magnetic latitudes. We estimated the longitudinal extent of magnetospheric ELF/VLF waves based on their occurrence rate. Our results showed that the ELF/VLF wave occurrence rate differed by twofold to threefold, depending on the longitudes of the observation sites. We explain this difference in terms of longitudinal differences in the ionosphere's magnetic field intensity, possibly due to the electron loss that occurs during the bounce motion at longitudes of small magnetic field intensity. Based on our statistical analysis, we estimated the typical longitudinal extent of ELF/VLF waves as ∼76°. Time series analysis results showed that the large longitudinal extent of the ELF/VLF waves occurs frequently during the main phase of geomagnetic storms and is also associated with substorms represented by the auroral electrojet index. Key Points The longitudinal extent of magnetospheric ELF/VLF waves was examined using six ground loop antennas at subauroral latitudes The typical extent of ELF/VLF wave are estimated as ∼ 76 degrees in longitude The longitudinal extent increased with geomagnetic activity