Forbush Decreases in the Cosmic-Ray Albedo Neutron Flux
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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 (<I>P<SUB>c</SUB></I>=1.24 GV) while the respective depressions on the OGO-6 neutron rates in the polar region (<I>P<SUB>c</SUB></I> < 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 <I>P<SUB>c</SUB></I>, < 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 -<I>mP<SUB>c</SUB></I>+<I>k</I>. Values of <I>m</I> and <I>k</I> 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.
- Earth, Planets and Space
Earth, Planets and Space 48(8), 1025-1031, 1996-08
Society of Geomagnetism and Earth, Planetary and Space Sciences