Study on the Energy Source of Small-Scale Ulf Waves in the Magnetosphere

Investigating the Relationship Between Energetic Particles and Small-Scale ULF Waves in the Magnetosphere

Abstract

It is assumed to date that the energy source of azimuthal small-scale ULF waves in the magnetosphere (azimuthal wave numbers m1) is provided by the energetic particles interacting with the waves through the bounce-drift resonance. In this paper we have solved the problem of the bounce-drift instability influence on the spatio-temporal structure of Alfven waves excited by a source of the type of ´ sudden impulse in a dipole-like magnetosphere. It is shown that the impulse-generated Alfven oscillation within a time ´ τ∼mT N (where T N is the toroidal eigenfrequency) is a poloidal one, and each field line oscillates with its own eigenfrequency that coincides with the poloidal frequency of a given L-shell. As time elapses, the wave becomes toroidally polarized because of the phase difference of the disturbance, and the oscillation frequency of field lines tends to the toroidal frequency.