Whistler Waves in the Young Solar Wind: Properties, Origin, and Consequences for Particles

Observations by the Parker Solar Probe mission of the solar wind at about 35 solar radii reveal the existence of whistler wave packets with frequencies below 0.1fce (20-150 Hz in the spacecraft frame). These waves bursts often coincide with local minima of the magnetic field magnitude observed in the vicinity of the switchbacks boundaries. The Poynting flux indicates sunward propagation that leads to a significant Doppler frequency downshift from 200-300 Hz to 20-80 Hz (from 0.2fce to 0.5fce). The polarization of these waves varies from quasi-parallel to significantly oblique. Their peak amplitude can be as large as 1-4 nT (up to 20% of the background magnetic field magnitude). The generation of these waves is supported by the modified electron distribution with increased transverse temperature anisotropy inside the magnetic hole. Sunward propagating whistler waves scatter the high energy solar wind electrons in the energy range up to 1 keV and potentially play a significant role in breaking the heat flux and scattering the Strahl population of suprathermal electrons into a halo population.