Second harmonics of auroral kilometric radiation observed by the Akebono satellite

概要

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The second harmonic wave properties of auroral kilometric radiation(AKR) were examined using data obtained by the Akebono satellite. The results of our statistical analysis indicate that the probability of a harmonic event occurrence is more than 60% of all AKR events. The relationship between the frequencies of the fundamentals and the second harmonics is exactly two times for the upper and lower cut-off frequencies of the spectra as well as the fine structures, within the resolution of the Akebono observations. The intensity ratio of the second harmonics to the fundamentals exhibits a two-fold nature, with both a linear and a quadratic relationship. Further data analyses also revealed that the second harmonic waves of AKR, which propagate in the X-mode, are generated from a source that is identical to that of the fundamental waves that propagate in the O-mode. These results suggest that the mechanism of AKR harmonic structure generation should allow the coexistence of different AKR emission processes.