Forbush Decreases in the Cosmic-Ray Albedo Neutron Flux

抄録

The Forbush decrease in the cosmic-ray albedo neutron flux has been measured by a neutron detector on board the OGO-6 satellite. For the events of June 7-10 and September 27-30, 1969, the Forbush decrease totalled 4.6 and 6% in amplitude respectively for the Mt. Washington neutron monitor (P_c=1.24 GV) while the respective depressions on the OGO-6 neutron rates in the polar region (P_c < 0.3 GV) were 5 and 9%. The depression in the OGO-6 neutron rates was larger at higher geomagnetic latitudes than at lower latitudes. These results indicate that Forbush decrease has greater effect on lower-energy charged particles, and that the phenomenon is reflected in the production of neutrons in the earth's atmosphere. However, it appears that the integrated effects of Forbush decreases on cosmic-ray albedo neutrons do not significantly decrease the CRAND source of charged particles in the radiation belt. For vertical cutoff rigidities P_c, < 1 GV, the total percent decrease in the OGO-6 neutron rates (≤10 MeV) during the Forbush decreases, 1969 June 7-10, September 27-30, and November 21-December 6 can be represented by -mP_c+k. Values of m and k are each constant for the particular Forbush decrease but increase with increasing Mt. Washington neutron monitor monthly average rates, an indication of a flattening of the rigidity dependence of Forbush decrease towards maximum solar modulation.