Whistler Wave Observations by Parker Solar Probe During Encounter 1: Counter-propagating Whistlers Collocated with Magnetic Field Inhomogeneities and their Application to Electric Field Measurement Calibration

Abstract

Observations of the young solar wind by the Parker Solar Probe (PSP) mission reveal the existence of intense plasma wave bursts with frequencies between 0.05 and 0.20f ce (tens of hertz up to ∼300 Hz) in the spacecraft frame. The wave bursts are often collocated with inhomogeneities in the solar wind magnetic field, such as local dips in magnitude or sudden directional changes. The observed waves are identified as electromagnetic whistler waves that propagate either sunward, anti-sunward, or in counter-propagating configurations during different burst events. Being generated in the solar wind flow, the waves experience significant Doppler downshift and upshift of wave frequency in the spacecraft frame for sunward and anti-sunward waves, respectively. Their peak amplitudes can be larger than 2 nT, where such values represent up to 10% of the background magnetic field during the interval of study. The amplitude is maximum for propagation parallel to the background magnetic field. We (i) evaluate the properties of these waves by reconstructing their parameters in the plasma frame, (ii) estimate the effective length of the PSP electric field antennas at whistler frequencies, and (iii) discuss the generation mechanism of these waves.

Switchbacks and Associated Magnetic Holes Observed near the Alfvén Critical Surface

“…The answer is that these rarefaction magnetic features represent non-Alfvénic behavior in an otherwise quasi-Alfvénic feature. These non-Alfvénic MH features at the switchback boundaries are associated with enhanced kinetic activity, including enhanced electron flows and electron plasma wave intensifications (Rasca et al 2022) and whistler waves during PSP's first encounter (Agapitov et al 2020;Karbashewski et al 2020;Froment et al 2023). In the work herein, we now suggest that these magnetic field rarefactions form mostly in the super-Alfvénic solar wind, which means that the associated kinetic activity forms mostly above the Alfvén critical surface, possibly in association with diamagnetic current flow.…”

“…Kinetic activity was also associated with many of these switchback boundary |B| dropouts, including an intensification of the plasma emissions near the local electron plasma frequency ( f pe ) and enhanced electron flows (Rasca et al 2022). Works looking at E1 also showed whistler waves associated with magnetic holes (MHs)/dropouts, which would originate from magnetic activity as well (Agapitov et al 2020;Karbashewski et al 2020;Froment et al 2023).…”

Reconstruction of Polarization Properties of Whistler Waves From Two Magnetic and Two Electric Field Components: Application to Parker Solar Probe Measurements

“…This figure is adapted from Figure 9 of Karbashewski et al. (2023). The polarization parameters are directly evaluated using measurements of the three magnetic field components and the missing component of the electric field is estimated from $$\vec{E}\mathrm{w}(\omega ,t)\cdot \vec{B}\mathrm{w}(\omega ,t)=0$$ (Figures 2c and 2e).…”

“…This figure is adapted from Figure 6 of Karbashewski et al. (2023). The polarization parameters and the missing component of the electric field are evaluated as in Section 3.1.…”

“…It should be noted that the form of Equations 2 and 3 shows that the method is independent of the chosen effective length of the antennas. In the following, we therefore take an effective length of 3.5 m, even though this length depends on the frequency and on the propagation direction (Karbashewski et al, 2023).…”