Gradient of cosmic-ray intensity perpendicular to the ecliptic plane

Abstract

Cosmic-ray gradients perpendicular to the ecliptic (cross-gradients) can be estimated, in principle, from the seasonal variation of cosmic-ray intensity, because the earth deviates from the solar equatorial plane by about ±7° heliolatitude (equivalent to ±1/8 A.U.) during a year. However, such estimates can be greatly vitiated by long-term cosmic-ray changes specially when these are nonlinear. Neutron monitor data for the period 1958–67 are critically examined for such an effect. The long-term changes were tolerably linear only during Sept. ’63-May ’65 and analysis for this period yields an extrapolated cross-gradient less than (4±2)%/A.U. For other periods the method is unreliable. The method is applicable only to heliolatitudes within ±7° corresponding to distances of ±1/8 A.U. and hence gives no information for regions beyond.