Processes associated with particle transport in corotating interaction regions and near stream interfaces

Abstract

Pioneer and Ulysses observations of energetic particles and solar wind plasma and magnetic fields are analyzed to study particle transport in corotating interaction regions (CIRs) and near stream interfaces (SIs). Energetic particle diffusion with a lowered coefficient near the SIs as compared with the free solar wind may account for the energetic particle profiles in CIRs and for the modulation of Jovian electrons. Our analyses include examination of the magnetic power and variances perpendicular and parallel to the magnetic field for a range of wave numbers and for a range of conditions within two CIRs. Since the magnetic field immediately on either side of a SI, but near it, is not connected to either the forward shock or reverse shock, it is the cross‐field motion of the energetic particles that is relevant. Since the cross‐field transport is thought to be related to field line mixing, or random walk, we examined magnetic field fluctuations normal to the average field to determine whether any signature of reduced perpendicular particle transport could be found. Evidence consistent with reduced particle transport near the SI was indeed found when we examined time series of the 1‐min averages of the magnetic field components. A planar magnetic structure was associated with the trailing unshocked layer following the SIs (i.e., SI to SI + 12 hours) and also with the entire CIRs, but it was not present in the free solar wind. We have quantitatively examined the effects of shear and compression on particle transport and conclude that the effects of shear and compression reduce particle transport in CIRs and in the vicinity of SIs.