Comparisons of ground-based monitor data with pioneers 8, 9, 10 and 11 observations in 1968-1974

We have examined ground-based neutron monitor data and the counting rates in different energy channels on the Pioneer 8, 9, 10 and 11 spacecraft from 1968-1969 to 1972-1974 to determine the scale size of the transient cosmic-ray variations (Forbush decreases) and the relationship of these variations to changes in the interplanetary magnetic field. Since the Pioneer spacecraft sampled the inner modulating region extensively, the spatial extent of Forbush decreases (Fd's) can be determined. In some cases the Fd modulating region was co-rotating and in others radially expanding. The azimuthal extent of the Fd region was variable but was typically approximately 450 in extent. These observations will be interpreted in terms of models proposed for Fds. (orig.)