Sporadic Geomagnetic Pulsations at Frequencies of up to 15 HZ in the Magnetic Storm of November 7–14, 2004: Features of the Amplitude and Polarization Spectra and their Connection with Ion–Cyclotron Waves in the Magnetosphere

Resumo

We study the dynamics of the geomagnetic-pulsation spectra at unusually high frequencies (including the frequencies exceeding the Schumann resonance frequency 8 Hz), which were detected for the first time at the Novaya Zhizn’ midlatitude station (the McIlwain parameter L = 2.6) at the time of a strong magnetic storm on November 07–14, 2004. To interpret the observed pulsation frequencies, we used the data from the NOAA low-orbit satellites which recorded localized precipitations of energetic protons (with energies of 30 to 80 keV) and calculations of the singlepass cyclotron amplification of electromagnetic ion–cyclotron waves. Amplitude and polarization characteristics of the radiation spectra at frequencies of up to 15 Hz at the Novaya Zhizn’ and Lovozero stations (L = 5.2) are compared. It is shown that the magnetic field oscillations in the frequency range 7–15 Hz correlate with proton precipitations and proton auroras at geomagnetic latitudes 50°–57° (L = 2.42–3.37). It is also shown that for a high anisotropy of the pitch-angle distribution of the ring-current protons at such low geomagnetic latitudes, the frequency spectrum of observed high-frequency radiation agrees well with the calculated location of the maximum of the single-pass cyclotron amplification of electromagnetic ion–cyclotron waves. Analysis of the data and calculation results has led to the conclusion that inherently the recorded signals are a high-frequency counterpart of the Pc1 pulsations and are due to the generation of ion–cyclotron waves in the magnetosphere at unusually low latitudes, which are probably stipulated by the shift of the plasma pause to these latitudes during a strong magnetic storm.