Measurements of cosmic ray anisotropies from Pioneers 10 and 11

A progress report is presented on cosmic ray anisotropy measurements performed in interplanetary space on the Pioneers 10 and 11. A directional Cerenkov counter, sensitive to protons and alpha particles with kinetic energies exceeding 480 MeV/nucleon, was used to determine east-west and north-south anisotropies. Large variations in anisotropies with a time scale of about 60 days were found for the period April-November 1973. The total data set shows an east-west anisotropy of 0.46 plus or minus 0.11% and a north-south anisotropy of 0.03 plus or minus 0.11%. This result for the east-west anisotropy is compatible with a large value of the ratio of the perpendicular to the parallel components of the diffusion coefficient.