Transport and Acceleration of Energetic Charged Particles near an Oblique Shock

We have developed a numerical simulation code that treats the transport andacceleration of charged particles crossing an idealized oblique,non-relativistic shock within the framework of pitch angle transport using afinite-difference method. We consider two applications: 1) to study thesteady-state acceleration of energetic particles at an oblique shock, and 2) toexplain observed precursors of Forbush decreases of galactic cosmic rays beforethe arrival of an interplanetary shock induced by solar activity. For theformer, we find that there is a jump in the particle intensity at the shock,which is stronger for more oblique shocks. Detailed pitch angle distributionsare also presented. The simple model of a Forbush decrease explains the keyfeatures of observed precursors, an enhanced diurnal anisotropy extendingseveral mean free paths upstream of the shock and a depletion of particles in anarrow loss cone at ~0.1 mean free path from the shock. Such precursors havepractical applications for space weather prediction.Comment: 20 pages + 12 figures, aas2pp4.sty included, to appear in Astrophys. J. (vol. 515, no. 2, April 20, 1999