Analysis of Pc5 Wave Modes Observed by CRRES and GOES Satellites During a Relativistic Electron Enhancement Event

A possible mechanism for relativistic electron acceleration in the magnetosphere is drift-resonance interaction with ULF waves. Effective acceleration is expected if there exists a resonant condition between the electron drift periods and wave periods, so that azimuthally drifting electrons will periodically experience the same electric perturbation fields and be accelerated. In order to confirm the acceleration mechanism, it is important to identify the wave mode responsible for the acceleration. We have made a detailed analysis of the perturbation electric and magnetic field data taken during a relativistic electron acceleration event [Tan et al., 2004]. We found that both toroidal and poloidal wave components are present in the ULF wave data and that both components have discrete frequency spectra that are consistent with the discrete Alfven wave spectra typically measured on the ground. By interpreting the relative phases of the observed perturbation field quantities in the context of global MHD wave structure in the magnetosphere, we have determined the CRRES and GOES spacecraft positions relative to the nodes of the magnetospheric MHD waves, and therefore determined the wave modes of the observed Pc5 waves. In this paper, we will describe our wave analysis and discuss the implications of our results on relativistic-electron acceleration in the magnetosphere. Tan, L. C., S. F. Fung, and X. Shao (2004), Observation of magnetospheric relativistic electrons accelerated by Pc-5 ULF waves, Geophys. Res. Lett., 31, L14802, doi:10.1029/2004GL019459.