Properties of daytime long-period pulsations during magnetospheric storm commencement

Abstract

Long-period geomagnetic pulsations during the SSC of July 14, 2012, are studied. The prenoon longitudinal sector (09:20–11:30) MLT, from the boundaries of which pulsations propagate azimuthally onto the dawn and dusk sides with an opposite polarization direction and increased amplitude, has been distinguished. The position of this sector relative to noon (a shift to the dawn side) depends on the front azimuthal inclination. It has been found that the polarization direction reverses in going from low (<30°) to middle/subauroral (≥50°) latitudes on the entire dayside. The geomagnetic pulsations mainly fluctuate near the f₁ = 2.9 and f₂ = 4.4 mHz frequencies. Fluctuations with frequency f₁, which coincide with the fluctuation frequency of the IMF х component, predominate at the polar cap latitudes (the open field line region) in the form of rapidly attenuating impulses and at low latitudes with a much smaller amplitude. Fluctuations with frequency f₂ are globally registered at all latitudes in the dayside sector below the magnetopause projection as a train of several fluctuations. It is assumed that fluctuations with frequency f₁ penetrate from the solar wind, and fluctuations with frequency f₂ are radial magnetopause oscillations.