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.