@article{oai:nipr.repo.nii.ac.jp:00000513,
 author = {Kokubun, Susumu and Hayashi, Kanji and Oguti, Takasi},
 journal = {JARE scientific reports. Series A, Aeronomy},
 month = {Mar},
 note = {P(論文), Observations of natural electromagnetic noise in the VLF range have been carried out at Syowa Station, Antarctica, since April, 1966. The VLF observation system is briefly described and the result on VLF emissions known as polar chorus is presented, based on the data obtained in 1966. It is confirmed that polar chorus in the auroral zone is a daytime phenomenon and that its occurrence culminates in the summer season. The statistical analysis indicates that a definite positive correlation exists between polar chorus activity and magnetic activity, especially during periods of moderate magnetic condition. Comparison of VLF data with magnetograms from low latitude stations reveals that VLF chorus variations are closely related to ssc, si and other worldwide magnetic changes, and that in several cases the chorus intensity decreases are associated with solar flares. Sudden impulse type magnetic field variations, which are thought to be caused by compression or expansion of the magnetosphere, are associated in most cases with polar chorus variation in the daytime, and a positive impulse is accompanied by a sudden enhancement or commencement of chorus, whereas a negative impulse is associated with a sudden decrease or fadeout of chorus emission. The center frequency of chorus tends to increase at the time of positive magnetic variations, and the rate of this frequency change is closely related to the magnitude of the corresponding magnetic variation. These characteristics are explained by electron cyclotron instability in the daytime magnetosphere, L=6～10.},
 pages = {1--34},
 title = {VLF Emission Study at Syowa Station,Antarctica -Polar Chorus Emission and Worldwide Geomagnetic Variation-},
 volume = {6},
 year = {1969}
}