ANISOTROPIES OF SOLAR COSMIC RAYS

The behavior of the anisotropy during solar cosmic-ray events is discussed in terms of a simple model in which cosmic-ray particles propagate along the mean interplanetary magnetic field, undergoing pitch-angle scattering. It is shown that a generalized form of the telegraph equation should be used when the anisotropy is large (i.e. greater than 30%), but that the usual diffusion equation is adequate otherwise. The behavior of the anisotropy during the decay phase of solar cosmic-ray events is then considered, and several effects which can give rise to a small persisting anisotropy are described. Finally, observations of solar cosmic-ray anisotropies following flares are reviewed and it is concluded that the simplified mathematical treatment presented here adequately describes some of the general features of the behavior of the anisotropy, but does not provide a detailed quantitative description of the particle behavior, especially during the highly anisotropic phase of an event. © 1969 D. Reidel Publishing Company.