Plasma Waves near the Electron Cyclotron Frequency in the near-Sun Solar Wind

Abstract

Data from the first two orbits of the Sun by Parker Solar Probe reveal that the solar wind sunward of 50 solar radii is replete with plasma waves and instabilities. One of the most prominent plasma wave power enhancements in this region appears near the electron cyclotron frequency (f_ce). Most of this wave power is concentrated in electric field fluctuations near 0.7 f_ce and f_ce, with strong harmonics of both frequencies extending above f_ce. At least two distinct, often concurrent, wave modes are observed, preliminarily identified as electrostatic whistler-mode waves and electron Bernstein waves. Wave intervals range in duration from a few seconds to hours. Both the amplitudes and number of detections of these near-f_ce waves increase significantly with decreasing distance to the Sun, suggesting that they play an important role in the evolution of electron populations in the near-Sun solar wind. Correlations are found between the detection of these waves and properties of solar wind electron populations, including electron core drift, implying that these waves play a role in regulating the heat flux carried by solar wind electrons. Observation of these near-f_ce waves is found to be strongly correlated with near-radial solar wind magnetic field configurations with low levels of magnetic turbulence. A scenario for the growth of these waves is presented which implies that regions of low-turbulence near-radial magnetic field are a prominent feature of solar wind structure near the Sun.

References in corpus (6)

• Whistler mode waves and the electron heat flux in the solar wind: Cluster observations
• Statistical Study of Whistler Waves in the Solar Wind at 1 AU
• Scattering of Strahl Electrons in the Solar Wind between 0.3 and 1 au: Helios Observations
• Experimental determination of whistler wave dispersion relation in the solar wind
• Suprathermal electron strahl widths in the presence of narrow-band whistler waves in the solar wind
• Beaming electromagnetic (or heat-flux) instabilities from the interplay with the electron temperature anisotropies

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• Statistics and Polarization of Type III Radio Bursts Observed in the Inner Heliosphere
• Electron heat flux in the near-Sun environment
• Particle-In-Cell simulation of whistler heat flux instabilities in the solar wind: heat flux regulation and electron halo formation
• Parker Solar Probe evidence for scattering of electrons in the young solar wind by narrowband whistler-mode waves
• Narrowband oblique whistler-mode waves: Comparing properties observed by Parker Solar Probe at <0.2 AU and STEREO at 1 AU
• Lepton-driven Non-resonant Streaming Instability
• Whistler Wave Observations by \textit{Parker Solar Probe} During Encounter $1$: Counter-Propagating Whistlers Collocated with Magnetic Field Inhomogeneities and their Application to Electric Field Measurement Calibration
• Reconciling Parker Solar Probe observations and magnetohydrodynamic theory
• Parker Solar Probe observations of near-$f_{\mathrm{ce}}$ harmonics emissions in the near-Sun solar wind and their dependence on the magnetic field direction
• Whistler waves in the young solar wind: statistics of amplitude and propagation direction from Parker Solar Probe Encounters 1-11