Application of wave distribution function methods to an ELF hiss event at high latitudes

Abstract

Multicomponent waveform data are used to calculate wave polarization and propagation characteristics, with both simple plane wave methods and more general wave distribution function (WDF) techniques. The WDF techniques allow us to estimate a continuous distribution of wave energy with respect to the wave vector directions. We describe several newly developed analysis methods, and we compare their results with existing techniques. This comparison allows us to reach a common interpretation of propagation properties and to exclude possible artifacts. The methods are applied to an electromagnetic ELF hiss event observed by the low‐altitude satellite Freja. A part of the emission can be described by simple plane wave methods. WDF techniques are, however, needed to fully characterize the wave propagation when the components of the wave magnetic field vector are not mutually coherent and the polarization degree is low. In this case we observe large peaks on the WDF shape or simultaneous propagation of downgoing and reflected upgoing waves. The WDF techniques also confirm that experimental polarization properties are consistent with their predictions by the cold plasma theory.