Scaling of field‐line random walk in model solar wind fluctuations

Gray, P. C.; Pontius, D. H.; Matthaeus, W. H.

doi:10.1029/96gl00769

Cited by 67 publications

(34 citation statements)

References 21 publications

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“…Kadomtsev & Pogutse (1979) also inferred Bohm diffusion, based on a dimensional argument related to what (in the present work) we term random ballistic decorrelation (RBD). For a two-component 2D+slab model of turbulence (to be described shortly) in which the 2D component dominates, the non-perturbative theory of Matthaeus et al (1995) predicted Bohm diffusion using the DD approach, which was confirmed in computer simulations by Gray et al (1996).…”

Section: Introductionmentioning

confidence: 75%

Magnetic Field Line Random Walk for Disturbed Flux Surfaces: Trapping Effects and Multiple Routes to Bohm Diffusion

Ghilea

Ruffolo

Chuychai

et al. 2011

ApJ

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The magnetic field line random walk (FLRW) is important for the transport of energetic particles in many astrophysical situations. While all authors agree on the quasilinear diffusion of field lines for fluctuations that mainly vary parallel to a large-scale field, for the opposite case of fluctuations that mainly vary in the perpendicular directions, there has been an apparent conflict between concepts of Bohm diffusion and percolation/trapping effects. Here computer simulation and non-perturbative analytic techniques are used to re-examine the FLRW in magnetic turbulence with slab and two-dimensional (2D) components, in which 2D flux surfaces are disturbed by the slab fluctuations. Previous non-perturbative theories for D ⊥ , based on Corrsin's hypothesis, have identified a slab contribution with quasilinear behavior and a 2D contribution due to Bohm diffusion with diffusive decorrelation (DD), combined in a quadratic formula. Here we present analytic theories for other routes to Bohm diffusion, with random ballistic decorrelation (RBD) either due to the 2D component itself (for a weak slab contribution) or the total fluctuation field (for a strong slab contribution), combined in a direct sum with the slab contribution. Computer simulations confirm the applicability of RBD routes for weak or strong slab contributions, while the DD route applies for a moderate slab contribution. For a very low slab contribution, interesting trapping effects are found, including a depressed diffusion coefficient and subdiffusive behavior. Thus quasilinear, Bohm, and trapping behaviors are all found in the same system, together with an overall viewpoint to explain these behaviors.

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Section: Introductionmentioning

confidence: 75%

Magnetic Field Line Random Walk for Disturbed Flux Surfaces: Trapping Effects and Multiple Routes to Bohm Diffusion

Ghilea

Ruffolo

Chuychai

et al. 2011

ApJ

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“…The influence of magnetic field-line random walk on the cross-field diffusion coefficient has received considerable attention in the past (e. g., Jokipii 1966;Jokipii and Parker 1968;Forman et al 1974;Forman 1977;Bieber and Matthaeus 1997;Matthaeus et al 1995;Gray et al 1996;Barghouty and Jokipii 1996). Numerical simulations of cross-field diffusion in fully three-dimensional magnetic turbulence were first performed by Jokipii (1994, 1999), who found, rather surprisingly, that the simulation results did not agree with previous theories.…”

Section: Cross-field Diffusion Including Field-line Random Walkmentioning

confidence: 99%

Large gradual solar energetic particle events

Desai

Giacalone

2016

Living Rev. Sol. Phys.

379

305

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Solar energetic particles, or SEPs, from suprathermal (few keV) up to relativistic (∼few GeV) energies are accelerated near the Sun in at least two ways: (1) by magnetic reconnection-driven processes during solar flares resulting in impulsive SEPs, and (2) at fast coronal-mass-ejection-driven shock waves that produce large gradual SEP events. Large gradual SEP events are of particular interest because the accompanying high-energy (>10s MeV) protons pose serious radiation threats to human explorers living and working beyond low-Earth orbit and to technological assets such as communications and scientific satellites in space. However, a complete understanding of these large SEP events has eluded us primarily because their properties, as observed in Earth orbit, are smeared due to mixing and contributions from many important physical effects. This paper provides a comprehensive review of the current state of knowledge of these important phenomena, and summarizes some of the key questions that will be addressed by two upcoming missions-NASA's Solar Probe Plus and ESA's Solar Orbiter. Both of these missions are designed to directly and repeatedly sample the near-Sun environments where interplanetary scattering and transport effects are significantly reduced, allowing us to discriminate between different acceleration sites and mechanisms and to isolate the contributions of numerous physical processes occurring during large SEP events.

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“…The particle and field line diffusion coefficients are calculated using a heliospheric turbulence spectrum with slab and 2D components (Gray et al, 1996). The turbulence spectrum is given as…”

Section: Modelsmentioning

confidence: 99%

The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents

Laitinen

Effenberger

Kopp

et al. 2018

J. Space Weather Space Clim.

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-Insights into the processes of Solar Energetic Particle (SEP) propagation are essential for understanding how solar eruptions affect the radiation environment of near-Earth space. SEP propagation is influenced by turbulent magnetic fields in the solar wind, resulting in stochastic transport of the particles from their acceleration site to Earth. While the conventional approach for SEP modelling focuses mainly on the transport of particles along the mean Parker spiral magnetic field, multi-spacecraft observations suggest that the cross-field propagation shapes the SEP fluxes at Earth strongly. However, adding cross-field transport of SEPs as spatial diffusion has been shown to be insufficient in modelling the SEP events without use of unrealistically large cross-field diffusion coefficients. Recently, Laitinen et al. [ApJL 773 (2013b); A&A 591 (2016)] demonstrated that the early-time propagation of energetic particles across the mean field direction in turbulent fields is not diffusive, with the particles propagating along meandering field lines. This early-time transport mode results in fast access of the particles across the mean field direction, in agreement with the SEP observations. In this work, we study the propagation of SEPs within the new transport paradigm, and demonstrate the significance of turbulence strength on the evolution of the SEP radiation environment near Earth. We calculate the transport parameters consistently using a turbulence transport model, parametrised by the SEP parallel scattering mean free path at 1 AU, l Ã k , and show that the parallel and cross-field transport are connected, with conditions resulting in slow parallel transport corresponding to wider events. We find a scaling s ';max ∝ð1=l Ã k Þ 1=4 for the Gaussian fitting of the longitudinal distribution of maximum intensities. The longitudes with highest intensities are shifted towards the west for strong scattering conditions. Our results emphasise the importance of understanding both the SEP transport and the interplanetary turbulence conditions for modelling and predicting the SEP radiation environment at Earth.

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Scaling of field‐line random walk in model solar wind fluctuations

Cited by 67 publications

References 21 publications

Magnetic Field Line Random Walk for Disturbed Flux Surfaces: Trapping Effects and Multiple Routes to Bohm Diffusion

Magnetic Field Line Random Walk for Disturbed Flux Surfaces: Trapping Effects and Multiple Routes to Bohm Diffusion

Large gradual solar energetic particle events

The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents

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