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Quiet time interplanetary cosmic ray anisotropies observed from Pioneer 10 and 11

1978; American Geophysical Union; Volume: 83; Issue: A4 Linguagem: Inglês

10.1029/ja083ia04p01633

2156-2202

W.-H. Ip, W. Fillius, A. Mogro‐Campero, L. J. Gleeson, W. I. Axford,

Dark Matter and Cosmic Phenomena

The University of California at San Diego Cerenkov counters on the Pioneer 10 and Pioneer 11 spacecraft are capable of detecting protons and alpha particles with kinetic energy T ≥ 480 MeV/nucleon and electrons with T ≥ 6 MeV. With these instruments we have made measurements of cosmic ray anisotropies in interplanetary space, using the Pioneer 11 detector between April 17 and November 31, 1973 (during which interval the spacecraft moved from 1.1 to 2.7 AU), and the Pioneer 10 detector between March 1 and November 31, 1974 (during which interval the spacecraft moved from 6.0 AU to 6.8 AU). From the Pioneer 11 data the east‐west anisotropy has been determined to be ξ ϕ * ≈ 0.41 ± 0.11%, and the north‐south anisotropy ξ θ * ≈ 0. The ratio of the perpendicular and parallel components of the diffusion coefficient (κ ⊥ /κ ∥ ) is on this basis estimated to be ≈ 0.26 ± 0.08%. From the Pioneer 10 data, ξ ϕ * ≈ 0.59 ± 0.18%, ξ θ * ≈ 0.25 ± 0.08%, and we estimate that κ ⊥ /κ ∥ ≈ 0.13 ± 0.04. The large value of ξ θ * obtained from Pioneer 10 suggests that there was a substantial component of cosmic ray streaming from north to south. A comparison of the anisotropy and magnetic field data suggests that such a north‐south anisotropy could be due at least in part to the gradient drift effect and perhaps in part to an additional streaming independent of the magnetic field polarity. To produce the observed value of ξ θ * from the gradient drift effect the radial gradient at this distance should have a value of ≈0.3 ± 0.3%/AU, which is not incompatible with the radial gradients obtained from direct measurements.