Wave mode identification via wave distribution function analysis

Abstract

Satellite observations of plasma waves are often analyzed within linear theory of an infinite, homogeneous and magnetized plasma. Important aspects of wave propagation, such as dispersion and polarization, can then be analyzed. However, even for this simplified plasma model, the structure of the eigenmodes is sometimes complex. For instance, several wave modes with different polarization may be allowed at the same frequency. One way of distinguishing between wave modes in real data is by using the polarization information contained in observed frequency spectra to reconstruct the energy density in wave vector space, also called the wave distribution function (WDF). The purpose of this presentation is to show how WDF analysis can be used for identifying wave modes in a case with two overlapping wave modes, and to compare the results obtained with two independently developed methods for reconstructing the WDF. For this purpose Freja observations of waves around the local proton gyrofrequency are analyzed.