Effects of displacement current on wave dispersion relation and polarization properties in auroral plasmas

In-situ observations from the FREJA magnetospheric research satellite and the Fast Auroral SnapshoT satellite have shown that plasma waves are frequently observed in the auroral plasma, which are believed to be fundamentally important in wave energy dissipation and particle energization. However, the effects of a displacement current on these waves have not been examined. Based on the two-fluid theory, we investigate the dispersion relation and polarization properties of fast, Alfven, and slow modes in the presence of a displacement current, and the effects of the displacement current on these waves are also considered. The results show that the wave frequency, polarization, magnetic helicity and other properties for the fast and Alfven modes are highly sensitive to the normalized Alfven velocity v(A) /c, plasma beta beta, and propagation angle theta, while for the slow mode the dependence is minor. In particular, for both fast and Alfven modes, the magnetic helicity is obviously different with and without the displacement current, especially for the Alfven mode with the helicity reversals from right-handed to left-handed when v(A) /c increases from 0 to 0.3. The charge-neutral condition of both fast and Alfven modes with frequencies larger than the proton cyclotron frequency is invalid in the presence of the displacement current. Moreover, the presence of the displacement current leads to relatively large magnetic compressibility for the Alfven mode and relatively large electron compressibility for the fast mode. These results can be useful for a comprehensive understanding of the wave properties and the physics of particle energization phenomena in auroral plasmas.