Investigation of Quasi-periodic VLF Emissions and their relation to Geomagnetic Micropulsations

Abstract

VLF emissions the signal strength of which changes with time with a period longer than the two hop whistler group delay are called long period VLF emission pulsations¹ or quasi-periodic (QP) VLF emissions². About 400 QP events were observed in the VLF emission data recorded on chart at Byrd Station in Antarctica during 6 months (February–April, September–November 1964). VLF emissions were recorded in the frequency range 1–2.4 kHz and in a narrow band centred on 8 kHz. Additional observations were occasionally made at 400 Hz. QPs have been observed on the two lower frequency channels, though not necessarily simultaneously. They have never appeared on the 8 kHz channel. QPs were observed mostly when Byrd Station was on the daylight side of the Earth. Periods of QPs range from 10 s (the lowest limit resolvable) to about 2 min and occasionally up to 10 min. A QP event usually lasts for several tens of minutes. Sometimes it lasts for only a few minutes and sometimes for a few hours.