Nonstationary pearl pulsations as a signature of magnetospheric disturbances

Abstract

Abstract. We analyse long-lasting (several hours) Pc1 pearl pulsations with decreasing, increasing or constant central frequencies. We show that nonstationary pearl events (those with either decreasing or increasing central frequency) are observed simultaneously with increasing auroral magnetic activity at the nightside magnetosphere while the stationary events (constant central frequency) correspond to quiet magnetic conditions. Events with decreasing central frequency are observed mostly in the late morning and daytime whereas events with increasing central frequency appear either early in the morning or in the afternoon. We explain the diurnal distribution of the nonstationary pearl pulsations in terms of proton drifts depending on magnetic activity, and evaluate the magnetospheric electric ®eld based on the variation of the central frequency of pearl pulsations.

Recent progress in understanding Pc1 pearl formation

“…Therefore, this seasonal dependence was related to variations in the position of the wave source. Such a conclusion is supported by the findings of Feygin et al (2000), Kerttula et al (2001) who analyzed the Pc-1 frequency variation on a scale of several hours and in the course of several geomagnetic storms, respectively. The study of the seasonal dependence of Pc-1 wave frequency supplemented earlier studies of its diurnal variations (e.g., Afanasyeva, 1978) and solar-cycle dependence (Fraser-Smith, 1970;Matveeva, 1987).…”

Quiet Time Structured Pc1 Waves Generated During Transient Foreshock

“…It is known that central frequency of Pc1 waves decreases with increasing latitude (or L shell; e.g., Feygin et al, ). Observations at two latitudinally spaced stations show that frequency bands were the same at MSTK and FSMI, within 0.4–0.6 Hz, both in the event‐1 (13:00–14:15 UT) and the event‐2 (15:30–16:15 UT).…”