Statistics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh42b05q&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SH42B-05
Statistics
2104 Cosmic Rays, 2114 Energetic Particles, Heliospheric (7514), 2118 Energetic Particles, Solar, 7514 Energetic Particles (2114)
Scientific paper
Statistics of test particle transport are obtained by computing test particle trajectories in model turbulence, represented by superposed static slab magnetic fluctuations, 2D magnetic fluctuations and a uniform background magnetic field. For different parameter regimes, we calculate statistics corresponding to perpendicular and parallel transport for time scales up to several thousand Vt/λ (particle speed*time/correlation scale). Diffusive behavior is obtained for parallel and perpendicular transport, and diffusion coefficients are computed in several different ways and compared with theoretical results, including quasilinear and nonperturbative scattering theories. Parallel diffusion is observed after a typical interval of Vt/λ > several hundred, for δ B/B = 0.1 and particles resonant in the mid-inertial range. Perpendicular diffusion coefficients agree well with quasilinear theory over a wide range of parameters at higher energies at times around Vt/λ ≈ 100. At later times, mean square perpendicular displacements drop to lower values, associated with parallel diffusion effects. The question as to whether there is a secondary regime of diminished diffusion, or on the other hand, a regime of subdiffusion (so called ``compound diffusion'') is examined in these numerical experiments. The issue is subtle from a numerical perspective because of the long integration times and the diffusive effects of roundoff and interpolation. As has been found earlier [1,2] low energy perpendicular transport departs from the Field Line Random Walk limit in the time frame of Vt/λ ≈ 100. Research supported in part by NASA grant NAG5-8134 (SEC Theory Program) and NSF grants ATM-9713595. [1] J Giacalone and J R Jokipii, Ap. J, 204, 520 (1999)[2] R Mace, J W Bieber and W H Matthaeus, Ap. J.(2000)
Bieber John W.
Matthaeus William H.
Qin Gan
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