Propagation Analysis of Electromagnetic Waves: Application to Auroral Kilometric Radiation

Abstract

We give a brief tutorial description of techniques for determination of wave modes and propagation directions in geospace, based on multi-component measurements of the magnetic and electric field fluctuations. One class of analysis methods is based on the assumption of the presence of a single plane wave and can be used to determine the direction of the wave vector. If the wave field is more complex, containing waves which simultaneously propagate in different directions and/or wave modes, the concept of the wave distribution function becomes important. It is based on estimation of a continuous distribution of wave energy with respect to the wave-vector direction. This concept can furthermore be generalized to the distribution of energy in different wave modes. As an example of analysis of satellite data, our emphasis is on application of these techniques to the high-frequency waves, for example to Auroral Kilometric Radiation (AKR). We analyze multicomponent data of the MEMO instrument obtained using multiple magnetic and electric antennas onboard the Interball 2 spacecraft. Results of different analysis techniques are compared. The intense structured AKR emission is found to propagate predominantly in the R-X mode with wave energy distributed in relatively wide peaks at oblique angles with respect to the terrestrial magnetic field. As expected, the AKR sources correspond to multiple active regions on the auroral oval.