Variation in Path Lengths of Turbulent Magnetic Field Lines and Solar Energetic Particles

Variation in Path Lengths of Turbulent Magnetic Field Lines and Solar Energetic Particles
Wirin Sonsrettee (Faculty of Engineering and Technology, Panyapiwat Institute of Management, Nonthaburi, Thailand), Piyanate Chuychai (National Astronomical Research Institute of Thailand, Chiang Mai, Thailand), Achara Seripienlert (National Astronomical Research Institute of Thailand, Chiang Mai, Thailand), Paisan Tooprakai (Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, Thailand), Alejandro S’aiz (Department of Physics, Faculty of Science, Mahidol University, Bangkok, Thailand), David Ruffolo (Department of Physics, Faculty of Science, Mahidol University, Bangkok, Thailand), William H. Matthaeus (Department of Physics and Astronomy, University of Delaware, Newark, DE, Bartol Research Institute, University of Delaware, Newark, DE), Rohit Chhiber (Department of Physics and Astronomy, University of Delaware, Newark, DE, Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD)
arXiv:2404.14718v1 Announce Type: new
Abstract: Modeling of time profiles of solar energetic particle (SEP) observations often considers transport along a large-scale magnetic field with a fixed path length from the source to the observer. Here we point out that variability in the turbulent field line path length can affect the fits to SEP data and the inferred mean free path and injection profile. To explore such variability, we perform Monte Carlo simulations in representations of homogeneous 2D MHD + slab turbulence adapted to spherical geometry and trace trajectories of field lines and full particle orbits, considering proton injection from a narrow or wide angular region near the Sun, corresponding to an impulsive or gradual solar event, respectively. We analyze our simulation results in terms of field line and particle path length statistics for $1^circtimes 1^circ$ pixels in heliolatitude and heliolongitude at 0.35 and 1 AU from the Sun, for different values of the turbulence amplitude $b/B_0$ and turbulence geometry as expressed by the slab fraction $f_s$. Maps of the most probable path lengths of field lines and particles at each pixel exhibit systematic patterns that reflect the fluctuation amplitudes experienced by the field lines, which in turn relate to the local topology of 2D turbulence. We describe the effects of such path length variations on SEP time profiles, both in terms of path length variability at specific locations and motion of the observer with respect to turbulence topology during the course of the observations.arXiv:2404.14718v1 Announce Type: new
Abstract: Modeling of time profiles of solar energetic particle (SEP) observations often considers transport along a large-scale magnetic field with a fixed path length from the source to the observer. Here we point out that variability in the turbulent field line path length can affect the fits to SEP data and the inferred mean free path and injection profile. To explore such variability, we perform Monte Carlo simulations in representations of homogeneous 2D MHD + slab turbulence adapted to spherical geometry and trace trajectories of field lines and full particle orbits, considering proton injection from a narrow or wide angular region near the Sun, corresponding to an impulsive or gradual solar event, respectively. We analyze our simulation results in terms of field line and particle path length statistics for $1^circtimes 1^circ$ pixels in heliolatitude and heliolongitude at 0.35 and 1 AU from the Sun, for different values of the turbulence amplitude $b/B_0$ and turbulence geometry as expressed by the slab fraction $f_s$. Maps of the most probable path lengths of field lines and particles at each pixel exhibit systematic patterns that reflect the fluctuation amplitudes experienced by the field lines, which in turn relate to the local topology of 2D turbulence. We describe the effects of such path length variations on SEP time profiles, both in terms of path length variability at specific locations and motion of the observer with respect to turbulence topology during the course of the observations.