  We investigate the relation between Forbush cosmic ray decrease recovery time
and coronal mass ejection transit time between the Sun and Earth. We identify
17 Forbush decreases from ground based neutron count rates between 1978 and
2003 that occur during the same phase in the solar cycle and can be associated
with single coronal mass ejections (CMEs) in the SOHO LASCO CME Catalog or
previously published reports, and with specific interplanetary coronal mass
ejections (ICMEs) crossing the vicinity of Earth. We find an anti-correlation
between Forbush recovery times and CME transit time that contradicts the
predictions of simple cosmic ray diffusive barrier models. The anti-correlation
suggests that the decay rate of ICMEs is anti-correlated with their travel
speed. Forbush recovery times range from seven times the transit time for the
fastest disturbance to a fifth the Sun-Earth transit time for the slowest. To
account for the large range of measured recovery times we infer that the
slowest disturbances must decay rapidly with radius whereas the fastest ones
must remain strong. The longest recovery times suggest that the fastest
disturbances in our sample decayed less rapidly with radius than the ambient
solar wind magnetic field strength.
