Auroral-Zone Geophysical Events and their Relationship to theMagnetosphere

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Studies were made of inter-relations among VLF-ELF-ULF radio noises, ionospheric absorption, geomagnetic variations and aurora at the South Pole, Byrd and Eights Stations, Antarctica. Semi-diurnal peaks in the above geophysical parameters were found : these peaks occurred within a few hours before magnetic noon and others a few hours before magnetic midnight. A geophysical event which takes place in the day sector is called a D (day) event and night sector an N (night) event. The N event is similar to AKASOFU's substorm. One N event consists of three phases called N-1,N-2 and N-3. Early in the evening the N-1 is the major part of the N event. In mid-evening, three phases co-exist. The N-3 is the dominant feature of the late evening N event. Observations made by the Injun III satellite showed that VLF hiss (main feature of the N-1) was observed at the boundary and beyond the region of trapped electrons in the dark sector. VLF chorus (main feature of N-3) was observed in the closed lines of force. From the above observations, we suggest that the physical characteristics of auroral zone are asymmetric with respect to the day-night major axis. VLF hiss and band-type aurora are the main features of the evening side (N-1). VLF chorus, ionospheric absorption, ULF and patchy and surface-like aurora are characteristics of a post-midnight region (N-3). The break-up (N-2) is the transition between N-1 and N-3.
国立極地研究所の論文
1967-02-00