Simultaneous observation of VLF phase and absorption anomalies at Syowa Station, Antarctica in association with magnetospheric substorms

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概要

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• Ionospheric disturbances associated with magnetospheric substorms were detected with VLF (ƒ=10.2 and 13.6kHz) radio wave propagation and a riometer simultaneously at Syowa Station, Antarctica. It is shown that the phase of the OMEGA REUNION signals (10.2 and 13.6kHz, La Reunion) advances significantly in association with geomagnetic bays and ionospheric absorptions. In correspondence to these disturbances, VLF phase anomalies are also observed on the OMEGA ALDRA signal (13.6kHz, Aldra, Norway) as received at Inubo, Japan. The conjugacy of occurrence of the VLF phase anomalies in the northern and southern hemispheres indicates that ionospheric disturbances responsible for VLF phase anomalies are caused by precipitation of energetic electrons from the magnetosphere. Local time characteristics of VLF phase and absorption anomalies are obtained from data recorded during a period from September 1,1980 to January 31,1981. Precipitation of energetic electrons responsible for VLF phase anomalies takes place predominantly in the evening sector peaked around 22 MLT, whereas electron precipitation responsible for absorption anomalies takes place in the morning sector peaked around 0230 and 0730 MLT. The discrepancy in these local time characteristics is due to a difference in height of the ionosphere responsible for the VLF phase anomaly (h<80km) and the ionospheric absorption (h=80-100km). It is suggested that absorption anomalies are caused by energetic electrons with energies>30keV and VLF phase anomalies by more energetic electrons with energies>300keV. This conclusion is confirmed qualitatively by observational facts that a significant phase anomaly is observed on the REUNION (10.2kHz) signal which is reflected from the lowermost part of the ionosphere, whereas no corresponding disturbances either on the REUNION (13.6kHz) signal and in ionospheric absorption.

• 国立極地研究所の論文

著者

• Kikuchi Takashi

  Radio Research Laboratory

• Nozaki Kenro

  Radio Research Laboratories

• Ohtani Akira

  Inubo Radio Wave Observatory, Radio Research Laboratories

• Kikuchi Takashi

  Radio Research Laboratories

• Ohtani Akira

  Inubo Radio Wave Observatory Radio Research Laboratories

関連論文

• Phase and amplitude of VLF Omega signals observed simultaneously at three stations in Iceland in association with magnetospheric substorms
• A case study of VLF phase and amplitude variation at 12.1 kHz (Aldra) in Iceland
• Simultaneous observation of VLF phase and absorption anomalies at Syowa Station, Antarctica in association with magnetospheric substorms
• VLF Phase Anomalies Associated with Substorm
• A new multimode FM/CW ionosonde
• Preliminary results of the multimode FM/CW ionosonde experiment

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