Drift motion and perpendicular diffusion of energetic particles in interplanetary space based on spacecraft data

A realistic model of the interplanetary magnetic field (IMF) is constructed based on measurements taken by Pioneer 10 magnetometer at 5 AU. Energetic particle (0.1 - 100 MeV) propagation in this field is studied by a computer simulation of its motion in order to calculate Ksub(perpendicular to), the perpendicular diffusion coefficient, and (Vsub(D)) the average drift velocity of an ensemble of particles. Determinations of Ksub(perpendicular to) lie in the range 3 x 1019 - 8 x 1020 cm2 s-1 for the energies considered and they show that perpendicular diffusion may be an important process at these heliodistances when compared with parallel diffusion results obtained by similar techniques, contrary to what was previously thought. Drift velocity calculations are very close to predictions of guiding centre theory (within 30%) suggesting that this theory can be applied in the IMF. This result shows that gradient and curvature drifts can be present even in a highly perturbed field and thus they can have some influence in cosmic ray modulation. (orig.)