Parker Solar Probe Proton Beams and Waves: Observations and Modeling

Abstract:

Parker Solar Probe (PSP) observations with Solar Probe Analyzer for Ions (SPAN-I) detects the 3D velocity distribution function (VDF) of protons and a particles with evidence of super-Alfvénic beams. The data is supplemented with FIELDS instrument that shows evidence of accompanying ion-scale wave storms, such as reported in Verniero et al. (2020). We report new coordinated wave-particle investigations focusing on the periods with the extensive existence of proton beams near PSP perihelion. We use the observed plasma parameters of the proton beam events to setup 2.5D hybrid model (2 spatial dimensions with 3D velocity and magnetic field components). In the model the protons and alpha particles are modeled kinetically with Particle In Cell (PIC) method, while electrons are treated as fluid. We investigate the relaxation of the drift instability due to the proton beam events, the generation of non-thermal VDFs and temperature anisotropy of protons, the effects of alpha particles, and the associated spectrum of magnetic fluctuations. The modeling results are in good agreement with PSP observations, and allow investigating the onset and the kinetic evolution of proton beam events for a range of observationally motivated solar wind plasma parameters.