Interrelationship between ELF noise intensities, geomagnetic pulsations, and electron precipitation pulsations.

Abstract

A data recording program was conducted in 1978 at sites in the College-Poker Flat, Alaska, region. Naturally-occurring noise at extremely low frequencies (ELF), 15Hz to 4.5kHz, was recorded, simultaneously with geomagnetic pulsations and precipitation pulsations as detected by a fast-response 30MHz riometer. The ELF intensity modulations (ELFIM), geomagnetic pulsations (GP), and riometer pulsations (RP) were compared for specific events.The principal finding was that the ELFIMs were significantly influenced by fluctuations in the ionospheric attenuation coefficient in some events. In an event occurring on September 28, 1978, the ELFIM spectrum was determined mainly by the ionospheric attenuation as indicated by the RP, the phase relations being correct for this interpretation. Two storm sudden commencement events showed characteristics consistent with the interpretation given for the September 28 event.The study neither proves nor disproves the existence of wave-particle interactions in the equatorial region of the field lines. However, in several events where the GPs were of Pc type (Pc 3, 4, 5), the GPs seemed to control certain peaks in the power spectra for ELFIMs, consistent with the existence of wave and particle interactions as predicted by CORONITI and KENNEL (1970). In events where the GPs were of Pi form, we believe that the precipitation pulsations contribute to the enhancement of certain spectral peaks in the GP spectrum by modulating the ionospheric conductivity, on the assumption that 3-dimensional current loops were the generators of the Pi signals.