Parallel and perpendicular diffusion of energetic particles in the near-Sun solar wind observed by Parker Solar Probe

2025/09/12 by Subashchandar, Nibuna Siranjeevi Madam, Zhao, Lingling, Shalchi, Andreas +6 · 1 citation
#FOS: Physical sciences #Space Physics (physics.space-ph)

paper · doi:10.48550/arxiv.2509.10648

Abstract

We investigate energetic particle diffusion in the inner heliosphere (approximately 0.06-0.3 AU) explored by Parker Solar Probe (PSP). Parallel (kappa_parallel) and perpendicular (kappa_perp) diffusion coefficients are calculated using second-order quasi-linear theory (SOQLT) and unified nonlinear transport (UNLT) theory, respectively. PSP's in situ measurements of magnetic turbulence spectra, including sub-Alfvenic solar wind, are decomposed into parallel and perpendicular wavenumber spectra via a composite two-component turbulence model. These spectra are then used to compute kappa_parallel and kappa_perp across energies ranging from sub-GeV to GeV. Our results reveal a strong energy and radial distance dependence in kappa_parallel. While kappa_perp remains much smaller, it can increase in regions with relatively high turbulence levels delta B / B0. To validate our results, we estimate kappa_parallel using the upstream time-intensity profile of a solar energetic particle event observed by PSP and compare it with theoretical values from different diffusion models. Our results suggest that the SOQLT-calculated parallel diffusion generally shows better agreement with SEP intensity-derived estimates than the classic QLT model. This indicates that the SOQLT framework, which incorporates resonance broadening and nonlinear corrections and does not require an ad hoc pitch-angle cutoff, may provide a more physically motivated description of energetic particle diffusion near the Sun.

Citations

• A detailed survey of the parallel mean free path of solar energetic particle protons and electrons
• Parallel Diffusion Coefficient of Energetic Charged Particles in the Inner Heliosphere from the Turbulent Magnetic Fields Measured by Parker Solar Probe
• Irregular proton injection to high energies at interplanetary shocks
• Turbulence in the Sub-Alfvénic Solar Wind
• The FIELDS Instrument Suite for Solar Probe Plus

Cited by

• Compressive Structures in the Foreshock of Collisionless Shocks

Related

• Parallel Diffusion Coefficient of Energetic Charged Particles in the Inner Heliosphere from the Turbulent Magnetic Fields Measured by Parker Solar Probe
• The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents
• Impact of solar magnetic field amplitude and geometry on cosmic rays diffusion coefficients in the inner heliosphere
• Cross-field transport and pitch-angle anisotropy of solar energetic particles in MHD turbulence
• Observations of Cross Scale Energy Transfer in the Inner Heliosphere by Parker Solar Probe