The Effects of Relative Drift Velocities Between Proton and He^(2+) on the Magnetic Spectral Signatures in the Plasma Depletion Layer

Magnetic spectrum of the electromagnetic ion cyclotron waves in the terrestrial plasma depletion layer （PDL） are sometimes observed to have a BIF （bifurcated） signature, where a diminution around 0.5Ωp with Ωp the proton gyrofrequency, occurs between two activity peaks in the spectrum. By one-dimensional hybrid simulations, the effect of relative drift velocities between protons and He2＋ on the magnetic spectral signatures in the PDL is studied. The results show that the relative drift velocity enhances the development of proton cyclotron waves and declines the development of helium cyclotron waves. The proton cyclotron waves are firstly excited, and followed by the excitation of helium cyclotron waves due to the increase in the relative drift velocity. Moreover, the boundary between two activity peaks gets obscure.