A study of polarization of irregular pulsations of diminishing period and their generation mechanism

Abstract

The polarization of irregular pulsations of diminishing period (IPDPs) observed in Iceland ( L = 6–7) and at Syowa has been investigated and some new findings have emerged: (1) the IPDP event which has so far been considered to be one single event, normally consists of a few Subelements (or slopes); and (2) in general the first major element occupying the lowest frequency range is left-handed circularly polarized and the second major element in the higher frequency range is right-handed polarized. A hypothesis is presented to account for these observational facts. The first fact is indicative of the nature of successive particle injections during a substorm. The protons with higher energy during the first injection seem to encounter the bulge of the plasmasphere or plasmatail in the local time (L.T.) sector of 15–18 h and at L = 6–8, which would result in the generation of ion cyclotron waves. This expectation is supported by observational fact, especially the left-handed circular polarization of the first element observed in Iceland. Furthermore, the delay time of drift of protons for the first injection in a time-dependent convection electric field is calculated, and is compared with the observed time delay and the slope of the fine structures. Then, if we suppose that protons with lower energy are injected during a subsequent burst, they meet the plasmapause body at L < 5 and at L. T. > 18 h and, due to the ionospheric duct propagation over the great distance between the generation region and observing stations, the polarization in Iceland would be right-handed, which is consistent with observations.