Generation of the high-m Alfven waves in the magnetosphere by the moving source: theory and experiments

Abstract:

The theory of generation of the high-m Alfven wave by substorm injected energetic particles in the magnetosphere is suggested. The wave is supposed to be emitted by an alternating current created by the substorm injected drifting particle cloud. 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. The spatio-temporal structure of the generated waves was calculated. The azimuthal phase speed of the wave coincides with the gradient-curvature drift velocity of the injected particles. This equality holds for the substorm-related waves statistically studied with SuperDARN radars by James et al. (2013). Experimental indication of this mechanism is a double change of the wave polarization: from mixed to poloidal to toroidal. This change was observed for several events observed with geostationary and THEMIS satellites. Moreover, the theory allows one to give interpretation of the equatorward phase motion of the high-m Alfven waves as observed with radars.