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Effective Magnetic Meridian for Cosmic Rays


RECENT latitude surveys of cosmic-ray intensity made with neutron intensity monitors appear to confirm an earlier suspicion that the dipole approximation to the Earth's magnetic field fails to account accurately for the observed distribution of cosmic rays over the Earth's surface1–3. This has been revealed as a result of the much greater latitude variation observed with these instruments compared with charged-particle detectors. The Lemaître–Vallarta theory of the geomagnetic effect predicts a minimum in the cosmic-ray intensity coincident with the geomagnetic equator. Simpson et al.2 have collected the available observations of the equatorial minimum and conclude that the ‘cosmic ray equator’ fits more accurately the equator of a dipole rotated about the Earth's axis 40°–45° to the west of the ‘best fit’ dipole. Rothwell and Quenby3, on the other hand, find the magnetic dip equator fits adequately, and suggest that the Earth's real field rather than the dipole approximation accounts for the observed distribution.

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  1. 1

    Rose, D. C., Fenton, K. B., Katzman, J., and Simpson, J. A., Canad. J. Phys., 34, 968 (1956).

  2. 2

    Simpson, J. A., Fenton, K. B., Katzman, J., and Rose, D. C., Phys. Rev., 102, 1648 (1956).

  3. 3

    Rothwell, P., and Quenby, J., Proceedings of the Varenna Conference, June 1957.

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