Small-Scale Gradients and Large-Scale Diffusion of Charged Particles
in the Heliospheric Magnetic Field
J. Giacalone, J. R. Jokipii
University of Arizona, Tucson, Arizona, 85721
J. E. Mazur
Aerospace Corporation, El Segundo, CA, 90245
We have carried out numerical simulations of the propagation of energetic
charged particles in a turbulent magnetic field similar to that observed
in the solar wind. If the particles are released impulsively near the sun,
in a region small compared with the field coherence scale (a solar flare,
for example), they exhibit characteristic fluctuations in intensity at 1 AU
(dropouts), associated with very-steep localized gradients. These numerical
simulations are quantitatively very similar to recent observations by the ACE
spacecraft and are the result of the convection of alternatively filled and
empty flux tubes past the spacecraft. These fluctuations occur naturally as
part of the particle transport in the same field which results in large-scale
cross-field diffusion and which has previously been used to study the
propagation of CIR-associated particles to high heliographic latitudes.