Semi-diurnal anisotropy of cosmic radiation in the energy range 1 to 200 Gev

Abstract

From an analysis of the data from the worldwide network of neutron monitor stations, the general characteristics of the yearly mean semi-diurnal component of cosmic radiation are derived. The mean semi-diurnal component in the energy range 1-200 Gev can be represented as [ΔJ (R)/J (R)] = 4 × 10⁻⁵ R cos² Λ, for R < 200 Gv, and [ΔJ(R)/J(R)] = 0, for R > 200 Gv. The semi-diurnal component has a maximum along a direction perpendicular to the direction of the mean interplanetary field vector, varies as the first power of rigidity, and varies as cos² Λ where Λ is declination. The phase and the amplitudes of the semi-diurnal component also seem to be practically invariant with time during the period 1958-1968. The mean properties of the semi-diurnal anisotropy are consistent with the hypothesis of a positive density gradient of cosmic ray intensity in a direction perpendicular to the plane of ecliptic.