Whistler Waves in the Inner Heliosphere

During its first 174 days at heliocentric distances less than 0.5 au, Parker Solar Probe encountered hundreds of narrowband electromagnetic wave bursts in the whistler frequency range. These events typically lasted on the order of minutes, although narrowband storms lasting longer than one hour were observed as well. The FIELDS instrument measures two components of the electric field and two components of the magnetic field of each wave - here we describe an analysis method for determining polarization and propagation direction with this limited information. The waves are shown to be circularly polarized and to rotate in a right-handed sense around the background magnetic field, confirming their identification as whistlers. Their propagation directions are shown to be approximately collinear with the background magnetic field, although ambiguity remains as to whether they are anti-parallel or parallel. Future data will allow the analysis method to resolve this ambiguity, which is a critical step toward identifying Doppler-shifted cyclotron resonances between the waves and strahl electrons.