Cosmic-ray propagation processes: 3. The diurnal anisotropy in the vicinity of 10 Mev/nucleon

Abstract

The results of a measurement of the anisotropic character of the cosmic radiation in the vicinity of 10 Mev/nucleon during 1965–1966 are presented. The periods considered were those during which solar flare cosmic-ray flare effects were not discernible in the data; that is, they are representative of the anisotropy that is responsible for the diurnal variation observed in the energy range 1–100-bev by detectors situated on the surface of the earth. The anisotropy in the vicinity of 10-Mev/nucleon exhibits maximum cosmic-ray flux from the approximate direction of the sun, this being at quadrature to that observed in the 1- to 100-bev energy range. This observation suggests that in the vicinity of 10 Mev/nucleon (a) the cosmic radiation exhibits a density gradient directed toward the sun, and (b) the 10-Mev/nucleon cosmic radiation was primarily of solar origin during the period under consideration. Consideration of these and earlier results suggests that (a) the direction of the cosmic-ray density gradient reversed between 107 and 109 ev during the period of sunspot minimum, and (b) the cosmic radiation in the range 107–1011 ev corotates with the sun.