Changes in cosmic ray propagation induced by corotating interaction regions

By simulating the trajectories for scatter free and diffusive propagation of relativistic cosmic rays in a model of the heliospheric magnetic fields containing a representation of corotating interaction regions (CIR's), it is found that, due to the large gradients associated with these compression regions, the motion is strongly affected and differs substantially from the predictions of current modulation theory. For positive (outward) northern hemisphere polarity, particles do not stream purely from high latitudes but can come from almost any latitude in the outer heliosphere; for negative polarity, many particles come along the current sheet (as predicted) but a second, equally important, population exists comprising particles that do not start on the current sheet but are brought to low latitudes by their interaction with CIR's. Thus, it is concluded that CIR's (and other large scale structures) cannot be ignored in analyses of cosmic ray modulation.