Transport and acceleration of energetic charged particles near an oblique shock

We have developed a numerical simulation code that treats the transport and acceleration of charged particles crossing an idealized oblique, nonrelativistic shock within the framework of pitch angle transport using a finite-difference method. We consider two applications: (1) to study the steady state acceleration of energetic particles at an oblique shock and (2) to explain observed precursors of Forbush decreases of Galactic cosmic rays before the arrival of an interplanetary shock induced by solar activity. For the former, we find that there is a jump in the particle intensity at the shock, which is stronger for more oblique shocks. Detailed pitch angle distributions are also presented. The simple model of a Forbush decrease explains the key features of observed precursors, an enhanced diurnal anisotropy extending several mean free paths upstream of the shock and a depletion of particles in a narrow loss cone within similar to 0.1 mean free path from the shock. Such precursors have practical applications for space weather prediction.