Cosmic ray evidence for a ring current

Abstract

Many observations show that low rigidity protons from solar flares are permitted entry at Minneapolis only during the main phase of magnetic storms. The measured energy is much below the normal Stormer cutoff at that time. This paper develops the idea that a ring current responsible for the main storm field reduces the Stormer cosmic-ray cutoffs. The model of the ring chosen is actually an azimuthal current on the surface of a sphere with current intensity proportional to sin θ where θ = colatitude. It is shown that this mathematical form permits great simplicity in the analysis and leads to essentially the same result as a diffuse ring corresponding to the actual trapped radiation. The magnetic moment of the ring required to produce the cutoff change can be provided by reasonable intensities of very low energy trapped radiation. It is shown that the cosmic-ray data permit one to evaluate both the moment (M′) and radius (R) of the ring, whereas the surface magnetic measurements determine only the quantity M′/R3. Since observation shows that the cosmic-ray cutoffs return to normal during the main phase, it must be assumed that the ring shrinks inward so that the surface field is maintained negative. Cosmic-ray evidence concerning the presence of a permanent ring current is discussed. Such a ring is measured directly by satellites during quiet times.