Abstract
Spatial-temporal and spectral features of ground geomagnetic pulsations in the frequency range of 1–5 mHz at the initial phase of a strong magnetic storm of the 24th cycle of solar activity (August 5–6, 2011, with a Dst-variation in the storm maximum of −110 nT) are analyzed. Large opposite in sign amplitudes of variations in IMF parameters (from −20 to +20 nT) at a high velocity of the solar wind (∼650 km/s) accompanied by intense bursts in solar-wind density (up to ∼50 cm−3) were distinctive feature of interplanetary medium conditions causing the storm. Geomagnetic Pi3 pulsations global in longitude and latitude and in-phase in the middle and equatorial latitudes were found. The onset of pulsation generation was caused by a pulse of dynamic pressure of the solar wind (∼20 nPa), i.e., by a considerable compression of the magnetosphere. The maximum (2–3 mHz) in the amplitude spectrum of near-equatorial pulsations coincided with the maximum of pulsations in the daytime polar cap. After the next jump of the dynamic pressure of the solar wind (∼35 nPa), an additional maximum appeared in the pulsation spectrum in the frequency band of ∼3.5–4.5 mHz. Global pulsations suddenly stopped after a sharp decrease in the solar-wind dynamic pressure and corresponding extension of the magnetosphere. The obtained results are compared with the time dynamics of the position and shape of the plasmapause.
Published Version
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