Particle Propagation Upstream of CIR Shocks

Abstract

The first high solar latitude pass of the Ulysses spacecraft revealed the presence of MeV particle increases up to latitudes above 60 degrees, well outside the CIR belt but associated in time with the regular passage of these plasma interfaces at more equatorial latitudes. The particle increases have been explained variously as due to diffusion from a field line connection with a CIR at a greater distance, perpendicular diffusion in latitude, propagation from the inner Corona or an acceleration process on a connecting field line. Numerical solutions to the 1-D propagation equation upstream of a CIR shock for reasonable diffusion mean free paths are shown here to limit the source of the increases to within about 2 AU of the CIR's, asssuming the CIR's either trap or accelerate energetic particles and they diffuse from the nearby CIR interface. The problem of allowing propagation from the CIR's is eased if the CIRs are located according to the predictions for the current sheet with a solar source surface at $2.5 R_{s}$, rather than at $3.25 R_{s}$. Energetic electron observations showing delays with respect to the CIR-associated ions suggest possibly an acceleration in the inner corona, rather than in the CIR-associated shock. A more likely explanation, however, is the ability of electrons to take a longer a longer route, from beyond the point of observation, than for that of the ions and yet arrive within a few days of CIR closest approach time.