Browsing by Author "J. R. Szalay"

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    Magnetic field line random walk and solar energetic particle path lengths: Stochastic theory and PSP/IS IS observations
    (2021-06-01) R. Chhiber; W. H. Matthaeus; C. M.S. Cohen; D. Ruffolo; W. Sonsrettee; P. Tooprakai; A. Seripienlert; P. Chuychai; A. V. Usmanov; M. L. Goldstein; D. J. McComas; R. A. Leske; J. R. Szalay; C. J. Joyce; A. C. Cummings; E. C. Roelof; E. R. Christian; R. A. Mewaldt; A. W. Labrador; J. Giacalone; N. A. Schwadron; D. G. Mitchell; M. E. Hill; M. E. Wiedenbeck; R. L. McNutt; M. I. Desai; California Institute of Technology; Chulalongkorn University; University of New Hampshire Durham; University of Maryland, Baltimore County (UMBC); Johns Hopkins University Applied Physics Laboratory; Mahidol University; The University of Arizona; Jet Propulsion Laboratory; NASA Goddard Space Flight Center; Princeton University; The University of Texas at San Antonio; The Bartol Research Institute; National Astronomical Research Institute of Thailand; Panyapiwat Institute of Management
    Context. In 2020 May-June, six solar energetic ion events were observed by the Parker Solar Probe/IS IS instrument suite at ≈0.35 AU from the Sun. From standard velocity-dispersion analysis, the apparent ion path length is ≈0.625 AU at the onset of each event. Aims. We develop a formalism for estimating the path length of random-walking magnetic field lines to explain why the apparent ion path length at an event onset greatly exceeds the radial distance from the Sun for these events. Methods. We developed analytical estimates of the average increase in path length of random-walking magnetic field lines, relative to the unperturbed mean field. Monte Carlo simulations of field line and particle trajectories in a model of solar wind turbulence were used to validate the formalism and study the path lengths of particle guiding-center and full-orbital trajectories. The formalism was implemented in a global solar wind model, and the results are compared with ion path lengths inferred from IS IS observations. Results. Both a simple estimate and a rigorous theoretical formulation are obtained for field-lines' path length increase as a function of path length along the large-scale field. From simulated field line and particle trajectories, we find that particle guiding centers can have path lengths somewhat shorter than the average field line path length, while particle orbits can have substantially longer path lengths due to their gyromotion with a nonzero effective pitch angle. Conclusions. The long apparent path length during these solar energetic ion events can be explained by (1) a magnetic field line path length increase due to the field line random walk and (2) particle transport about the guiding center with a nonzero effective pitch angle due to pitch angle scattering. Our formalism for computing the magnetic field line path length, accounting for turbulent fluctuations, may be useful for application to solar particle transport in general.
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    Observations of Energetic-particle Population Enhancements along Intermittent Structures near the Sun from the Parker Solar Probe
    (2020-02-01) Riddhi Bandyopadhyay; W. H. Matthaeus; T. N. Parashar; R. Chhiber; D. Ruffolo; M. L. Goldstein; B. A. Maruca; A. Chasapis; R. Qudsi; D. J. McComas; E. R. Christian; J. R. Szalay; C. J. Joyce; J. Giacalone; N. A. Schwadron; D. G. Mitchell; M. E. Hill; M. E. Wiedenbeck; R. L. McNutt; M. I. Desai; Stuart D. Bale; J. W. Bonnell; Thierry Dudok De Wit; Keith Goetz; Peter R. Harvey; Robert J. MacDowall; David M. Malaspina; Marc Pulupa; M. Velli; J. C. Kasper; K. E. Korreck; M. Stevens; A. W. Case; N. Raouafi; California Institute of Technology; Universite d'Orleans; University of Minnesota Twin Cities; Space Sciences Laboratory at UC Berkeley; University of New Hampshire Durham; University of California, Los Angeles; University of Michigan, Ann Arbor; University of California, Berkeley; University of Maryland, Baltimore County; University of Delaware; Queen Mary, University of London; Johns Hopkins University Applied Physics Laboratory; Imperial College London; Mahidol University; The University of Arizona; Smithsonian Astrophysical Observatory; NASA Goddard Space Flight Center; Princeton University; University of Texas at San Antonio; The Bartol Research Institute; University of Colorado Boulder
    © 2020. The American Astronomical Society. All rights reserved.. Observations at 1 au have confirmed that enhancements in measured energetic-particle (EP) fluxes are statistically associated with "rough" magnetic fields, i.e., fields with atypically large spatial derivatives or increments, as measured by the Partial Variance of Increments (PVI) method. One way to interpret this observation is as an association of the EPs with trapping or channeling within magnetic flux tubes, possibly near their boundaries. However, it remains unclear whether this association is a transport or local effect; i.e., the particles might have been energized at a distant location, perhaps by shocks or reconnection, or they might experience local energization or re-acceleration. The Parker Solar Probe (PSP), even in its first two orbits, offers a unique opportunity to study this statistical correlation closer to the corona. As a first step, we analyze the separate correlation properties of the EPs measured by the Integrated Science Investigation of the Sun (ISo˙IS) instruments during the first solar encounter. The distribution of time intervals between a specific type of event, i.e., the waiting time, can indicate the nature of the underlying process. We find that the ISo˙IS observations show a power-law distribution of waiting times, indicating a correlated (non-Poisson) distribution. Analysis of low-energy (∼15 - 200 keV/nuc) ISo˙IS data suggests that the results are consistent with the 1 au studies, although we find hints of some unexpected behavior. A more complete understanding of these statistical distributions will provide valuable insights into the origin and propagation of solar EPs, a picture that should become clear with future PSP orbits.