Isotropic and anisotropic cosmic ray variations in March–June 1991

Abstract Through March–June 1991 the rigidity spectrum of isotropic variation and three-dimensional anisotropy of cosmic rays (CR) were obtained for each hour by the data of 38 neutron monitors. The maximum variation of 10 GV CR density is >36% with very hard spectrum (index ≈ 0.4). The average vector of CR anisotropy for these four months has a magnitude (≈0.6%) and direction (94°) as typical for cycle 22. Forbush decreases (FDs) in this period are characterised by complicated structure caused by the simultaneous action of numerous transients. Estimations of anisotropy and spatial CR gradients on the recovery phase of Forbush decreases indicate the existance of closed and open structures in the heliomagnetosphere.