Perpendicular propagation of magnetosonic waves

Abstract

Azimuthal and radial propagation characteristics of perpendicularly propagating fast magnetosonic waves in an axis‐symmetrical medium with the presence of plasmapause is investigated analytically based on Snell's law. We find thatQ = nr sin ψ is conserved during the propagation, where n is wave refractive index, ris geo‐centered distance, andψ is wave azimuthal angle with zero pointing radially outward. The radial range of wave propagation can be determined by comparing Q and the radial profile of nr.Trapped waves, which are bounded in a narrow radial range but migrate azimuthally and even circularly, are identified inside the plasmapause over a broad range of wave azimuthal angles and over a broad range of wave frequencies from the proton gyrofrequency to the lower hybrid resonance frequency. In contrast untrapped waves launched inside and outside the plasmasphere can travel azimuthally 0–4 hrs and 0–7 hrs in local times respectively. The substantial radial and azimuthal propagation may account for the presence of magnetosonic waves away from the source region.