The Field Line Resonance in the Three‐Dimensionally Inhomogeneous Magnetosphere: Principal Features

The paper is devoted to study of the field line resonance in the three‐dimensionally inhomogeneous model of the magnetosphere taking into account the plasma inhomogeneity across the magnetic shells, along the field lines and in the azimuthal direction. The emphasis is made on the azimuthally small scale modes since they allow approximate analytical investigation. It was found that the Alfvén mode can propagate only in a channel bounded by the toroidal and poloidal surfaces where the wave's frequency matches the toroidal and poloidal eigenfrequency, correspondingly. The resonance surface is located inside the channel. It is a separatrix dividing energy flows from the toroidal and poloidal surfaces. The separatrix is a surface where the wave energy is accumulated. The approach to the separatrix surface is accompanied by decrease of the azimuthal wavelength up to zero, the crossing is accompanied by jump of the wave amplitude. The wave amplitude on the resonance surface remains finite. Key Points In three‐dimensional inhomogeneous magnetosphere the Alfvén mode can propagate only in a channel inclined with respect to the magnetic shells The place of the energy accumulation is located inside the channel. This place have role a resonance surface in three‐dimensional model Near the resonance surface the radial wavelength goes to zero, but the wave amplitude remains finite