Polarization Properties of Whistler Waves From the First 17 Parker Solar Probe Encounters

Abstract

We present statistics on the polarization properties of whistler waves in the solar wind down to 0.05 AU (10.75 RS) using data from Parker Solar Probe's first 17 encounters. These properties were previously uncharacterized due to a technical issue affecting one component of the search-coil magnetometer after Encounter 1. Using a reconstruction technique, we show that whistlers are predominantly quasi-parallel to the magnetic field across all distances and propagation directions, with 87% exhibiting a propagation angle relative to the background magnetic field $\left(\theta \right)$ below 25$°$. Waves with $\theta$ above 25$°$ are observed with significantly lower amplitudes. Sunward whistlers (including counter-propagating (CP) cases, where anti-sunward waves are observed at the same time) statistically exhibit higher normalized amplitudes and frequencies than anti-sunward whistlers. We discuss generation mechanisms and wave-particle interactions. Specifically, CP sunward and sunward waves interact via less efficient resonances with Strahl electrons ($\gtrsim 300$ eV).