PC1 with a broad frequency spectrum — “Goose pulsations”

Abstract

Geomagnetic pulsations in the frequency range of Pc1 pearl waves with the dynamic spectra having a very narrow spectrum width at the beginning of the event and a very broad spectrum width (Δf/f0 ∼ 1) in the later part of the event are analyzed. One of the observed events shown by the dynamic spectrum resembles a goose with the beak at the beginning of the event and with the wing in the later part of the event. Various interpretations of these geomagnetic pulsations are presented taking into account nonlinear effects, quasilinear interaction of electromagnetic ion-cyclotron waves with energetic, anisotropic protons and modulation of plasma parameters in the magnetosphere by Pc3–5 hydromagnetic waves. The ionospheric effect in the signal formation is determined by the ionospheric Alfven resonator. It can control the frequency range of the dynamic spectra, but not the internal structure of the signal.