Dynamics of Low-Frequency Oscillations of the Magnetic Field and Solar-Wind Ion Flux Upstream of an Interplanetary Shock

Wave trains of magnetic field and ion-flux oscillations generated upstream of the ramp of interplanetary (IP) shock were studied according to BMSW plasma-spectrometer measurements of energy–time spectra of the solar-wind ions supplemented by magnetic-field measurements. It was shown that oscillations of the magnetic field upstream of the ramp of IP shock are accompanied by oscillations of the ion flux. A detailed analysis of two cases is carried out, and the results of statistical study are presented. Right-handed circular or elliptical polarization was observed in all wave trains of magnetic-field oscillations, which is consistent with the characteristics of magnetosonic oscillations corresponding to the low-frequency branch of whistler waves. It was obtained that the mean angles between the propagation direction of whistler waves relative to the magnetic field and shock normal direction were 31° and 40°, respectively. This result suggests that the wave packets upstream of the ramp of IP shock had the properties of propagating whistler waves. It was found that, on average, with an increase in the angle of propagation of whistler waved relative to the shock normal direction θkn, the angle between the wave vector and magnetic-field direction θkB decreases.