Interrelationship of cosmic-ray anisotropies and the interplanetary magnetic field

The direction of the cosmic-ray anisotropy during solar proton events and the concurrent direction of the interplanetary magnetic field vector are compared, using data obtained in 1966 by the Pioneer 6 spacecraft. It is shown that the nonequilibrium cosmic-ray anisotropy (normally observed to exhibit an amplitude in the range 20–50%) is field-aligned, while the equilibrium anisotropy (normally observed to exhibit an amplitude in the range 5–15%) is independent of the direction of the magnetic field vector. Two anomalous proton events during which pronounced anisotropies were observed with their maximum cosmic-ray fluxes directed toward the sun are discussed. It is shown that during these proton events there were synchronous reversals of 180° in the direction of the magnetic field vector and the cosmic-ray anisotropy in association with the passage of a magnetic sector boundary past the spacecraft. These observations are interpreted as possible evidence for there being a complex loop in the magnetic field.