Cosmic Radiation in the Trapped Orbits of a Solar Magnetic Dipole Field

Abstract

One of the well-known consequences which would follow from the existence of an appreciable solar magnetic dipole field is a diurnal variation in cosmic-ray intensity at intermediate latitudes on the earth. For the purpose of calculating the expected diurnal effect, it is first necessary to determine the extent to which the bounded orbits of the solar field are filled by the mechanism which has been discussed by Kane, Shanley, and Wheeler: namely, the scattering of cosmic-ray particles into bounded orbits as a result of magnetic deflection in the earth's field. A calculation of this effect is carried out here along the lines indicated by Kane, Shanley, and Wheeler but with several modifications. A solar dipole moment of 6.5\ifmmode\times\else\texttimes\fi{}${10}^{33}$ gauss-${\mathrm{cm}}^{3}$, which is implied by the latitude cutoff at the earth, is adopted for the calculations. The cosmic-ray intensity in the trapped orbits is found to be appreciably smaller than indicated in the earlier calculations. Correspondingly, it is expected that the diurnal effect at the earth will be larger than the currently accepted theoretical values. The apparent experimental absence of the effect, although not conclusive, casts doubt on the existence of a solar dipole field as large as 6.5\ifmmode\times\else\texttimes\fi{}${10}^{33}$ gauss-${\mathrm{cm}}^{3}$. The present work also provides an estimate of the average time which a cosmic-ray particle would spend in the trapping region. The value 5000 years, previously given, is revised downward by an order of magnitude.