Alfvan ship waves: High-m ULF pulsations in the magnetosphere generated by a moving plasma inhomogeneity

Abstract

The generation of a high-m Alfvn wave by substorm injected energetic particles in the magnetosphere is studied. The wave is supposed to be emitted by an alternating current created by the drifting particle cloud or ring current inhomogeneity. It is shown that the wave appears in some azimuthal location simultaneously with the particle cloud arrival at the same spot. The value of the azimuthal wave number is determined as m∼ω/ωd, where ‰ is the eigenfrequency of the standing Alfv̧n wave and ωd is the particle drift frequency. The wave propagates westward, in the direction of the proton drift. Under the reasonable assumption about the density of the energetic particles, the amplitude of the generated wave is close to the observed amplitudes of poloidal ULF pulsations.