VLF-LF Hiss Emissions Associated with Aurora

• Main Author: Makita, Kazuo
• Language: English
• Published: 1979
• Subjects: Mizuho; Syowa Station; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/record/471/files/KJ00000011176.pdf

P(論文) It is shown that auroral hiss emissions observed in high latitudes can be categorized into two types on the basis of the power spectrum and its temporal variation. They are called the narrow-band continuous hiss and the wide-band impulsive hiss. The continuous hiss has a narrow frequency range with a center frequency of about 10 kHz and a band width of a few kHz and is characterized by a long time duration (longer than a few tens of minutes). The impulsive hiss, on the other hand, has a wide frequency range with a spectral peak frequency of about 10 kHz and a band width of a few tens of kHz and is of a short time duration (usually shorter than 10 minutes). On the basis of observations at the two Stations, Syowa and Mizuho and the ISIS 2 satellite, the continuous hiss emissions are found usually to occur associated with the steady auroral arc located near the poleward horizon of Syowa Station, and the impulsive hiss emissions, on the other hand, are found to occur accompanying the initial brightening of active aurora (corona, rayed-band, west-ward traveling surge) that appeared near the zenith. These relationships between two types of hiss and the global auroral activity are confirmed by the comparison between the global auroral data observed on the DMSP satellite and the ground data of hiss. A systematic local time variation of the arrival direction of the continuous hiss emissions is also found. It is shown that the arrival direction in early evening (18h-19h) is the east and it changes from east to west around 20h-21h. This local time variation of the arrival direction will be discussed in relation to the statistical distribution of the source region of the continuous hiss emissions. The arrival direction of the waves was next examined and it shows that the continuous hiss arrives from several hundreds of km equatorward of the related aurora, while the impulsive hiss sometimes arrives from the region nearer the auroral location. It also becomes clear that the distance between the exit (the arrival ...