LAUSR

Large-amplitude electromagnetic ion cyclotron (EMIC) waves induce unique dynamics of charged particle movement in the magnetosphere. In a recent study, modulation of the ion pitch angle in the presence of large-amplitude EMIC waves is observed, and a good explanation for this phenomenon is lacking. In this paper, we investigate this modulation primarily via a one-dimensional hybrid simulation model. We find that the modulation is caused by the bulk velocity triggered by large-amplitude EMIC waves. Affected by the bulk velocity, the number density of ions will enhance around a pitch angle of ∼ 90 °. Beyond that, the ion pitch angle is also modulated by the EMIC waves, and the modulation period is half of the EMIC waves' period. In addition, parameters that affect ion pitch angle modulation, including the wave amplitude, ion energy, ion species, and wave normal angle, are studied in this paper.