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| Main Authors: | , , , , , , , , |
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| Format: | Preprint |
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2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2509.10648 |
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| _version_ | 1866908537530089472 |
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| author | Subashchandar, Nibuna Siranjeevi Madam Zhao, Lingling Shalchi, Andreas Zank, Gary Paul Roux, Jakobus Le Li, Hui Zhu, Xingyu Silwal, Ashok Guzman, Juan Gabriel Alonso |
| author_facet | Subashchandar, Nibuna Siranjeevi Madam Zhao, Lingling Shalchi, Andreas Zank, Gary Paul Roux, Jakobus Le Li, Hui Zhu, Xingyu Silwal, Ashok Guzman, Juan Gabriel Alonso |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_10648 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Parallel and perpendicular diffusion of energetic particles in the near-Sun solar wind observed by Parker Solar Probe Subashchandar, Nibuna Siranjeevi Madam Zhao, Lingling Shalchi, Andreas Zank, Gary Paul Roux, Jakobus Le Li, Hui Zhu, Xingyu Silwal, Ashok Guzman, Juan Gabriel Alonso Space Physics 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. |
| title | Parallel and perpendicular diffusion of energetic particles in the near-Sun solar wind observed by Parker Solar Probe |
| topic | Space Physics |
| url | https://arxiv.org/abs/2509.10648 |