Interaction between ELF‐VLF emissions and magnetic pulsations: Regular period, ELF‐VLF pulsations and their geomagnetic conjugacy

Abstract

The characteristics of intensity modulations of quasi‐periodic (QP) VLF emissions and their relationships to magnetic variations are examined by using data obtained from Syowa and Mizuho Stations in Antarctica and at Husafell in Iceland, which is located near the geomagnetic conjugate point of Syowa. As shown in the previous studies, QP emissions can be classified into two types, according to whether emissions are closely associated with magnetic pulsations or not. It is found that the frequency of intensity modulations of type 2 QP's, without corresponding magnetic pulsations, is more stable that of type 1 QP's, associated with magnetic pulsations. In most cases magnetic variations during type 2 QP events, which occur under magnetically quiet condition, have no spectral peak corresponding to the peak in QP's spectrum. However, a small but significant peak in pulsation spectrum is occasionally noted, when the type 2 QP event occurs in a moderately disturbed condition. The peak value of magnetic spectrum, in such a case, is generally two orders of magnitude less than the maximum power of background magnetic fluctuations. The amplitude of magnetic pulsations is in the order of 0.01 nT/s. The H component of magnetic pulsations tends to be more correlated with the VLF intensity variations than the D component. These properties are observed at conjugate pair stations with good conjugacy. It is suggested that weak magnetic pulsations, correlated with the type 2 QP, are produced by ionospheric conductivity changes associated with wave induced particle precipitations.