Characteristics of Forbush-type cosmic ray intensity decreases observed during solar cycle 21

Preliminary cosmic-ray data from four sea-level neutron monitors for the Forbush-type decreases of solar cycle 21 are analyzed. Pressure-corrected profiles of the monthly and hourly mean cosmic ray intensities at the four different monitoring sites are given in a series of tables. Analysis of the data showed that the functional form of the decreases was essentially the same as in solar cycle 20. Comparison with data for the Forbush decrease of April 30, 1978 showed that the solar polar magnetic field reversal of 1980 had little effect on the long-term or short-term cosmic-ray modulation processes. The preliminary results are found to be in rough agreement with Pioneer 10 measurements of the radial gradient out to a distance of 20 AU.