Random Walk and Trapping of Interplanetary Magnetic Field Lines: Global Simulation, Magnetic Connectivity, and Implications for Solar Energetic Particles
Abstract
The random walk of magnetic field lines is an important ingredient in understanding how the connectivity of the magnetic field affects the spatial transport and diffusion of charged particles. As solar energetic particles propagate away from nearsolar sources, they interact with the fluctuating magnetic field, which modifies their distributions. We develop a formalism in which the differential equation describing the field line random walk contains both effects due to localized magnetic displacements and a nonstochastic contribution from the largescale expansion. We use this formalism together with a global magnetohydrodynamic simulation of the innerheliospheric solar wind, which includes a turbulence transport model, to estimate the diffusive spreading of magnetic field lines that originate in different regions of the solar atmosphere. We first use this model to quantify field line spreading at 1 au, starting from a localized solar source region, and find rms angular spreads of about 20°60°. In the second instance, we use the model to estimate the size of the source regions from which field lines observed at 1 au may have originated, thus quantifying the uncertainty in calculations of magnetic connectivity; the angular uncertainty is estimated to be about 20°. Finally, we estimate the filamentation distance, i.e., the heliocentric distance up to which field lines originating in magnetic islands can remain strongly trapped in filamentary structures. We emphasize the key role of slablike fluctuations in the transition from filamentary to more diffusive transport at greater heliocentric distances.
 Publication:

The Astrophysical Journal
 Pub Date:
 February 2021
 DOI:
 10.3847/15384357/abd7f0
 arXiv:
 arXiv:2011.06620
 Bibcode:
 2021ApJ...908..174C
 Keywords:

 Solar energetic particles;
 Interplanetary turbulence;
 Interplanetary magnetic fields;
 Solar wind;
 1491;
 830;
 824;
 1534;
 Physics  Space Physics;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Plasma Physics
 EPrint:
 doi:10.3847/15384357/abd7f0