The structure of field line resonances in a dipole magnetosphere with moving plasma

Abstract

A theoretical model of field line resonance in the magnetosphere with a dipole magnetic field and moving plasma was constructed. Motion of medium was simulated by its azimuthal rotation. Analytical and numerical solutions were found for MHD equations describing the structure of field line resonances. It was shown that a monochromatic, fast magnetosonic wave can excite several harmonics of standing Alfvén waves on different resonant surfaces at once. The resonant surface density is maximum in the transition layer at the magnetopause. The resonant oscillation amplitude profile becomes asymmetric in our model in regions with a maximum gradient of the background plasma velocity (plasmapause and magnetopause), in contrast to models with immobile plasma. In the same regions, the phase of resonant oscillations varies non-monotonically across the resonant surface which may serve as a detector of such regions in geomagnetic pulsation observations.