ELF emissions observed at Moshiri

Abstract

MORPHOLOGICAL characteristics of ELF emissions (frequency 2–3 kHz) observed at a low latitude ground station of Moshiri in Japan (geomag. lat. 34.5°N; L = 1.59) are reported here. ELF emissions in this frequency range are most poorly understood in the magnetospheric wave phenomena, and the information obtained on the ground will be of crucial importance in the study of their generation and propagation mechanisms. We have been observing VLF and ELF emissions at Moshiri^1–3 since 1964. We believe that Moshiri is at a lower latitude than any other where the emissions are continuously recorded⁴. Emissions of the hiss type are measured, by the minimum detection method¹, at four specific frequencies of 8 (Δƒ = ±1.25 kHz), 5 (±1 kHz), 1.5 (±.1 kHz) and 0.8 (±0.1 kHz) kHz, and recorded on paper charts. Wide band (0–10 kHz) observations on magnetic tapes have also been conducted following the synoptic schedule of two minutes every hour. We have found, using Ariel 3 VLF data, that the storm-time VLF emissions at Moshiri are generated around the plasmapause by the electron cyclotron instability with ring current electrons⁵. But the large number of VLF emissions appearing during magnetically quiet times have not been well studied². Satellite measurements made on board Pogo (I. Kimura, personal communication) and Isis⁶ have yielded a new type of ELF emissions (ƒ < 3 kHz).