Cosmic radiation in the heliosphere at successive solar minima 4. Modulation of galactic cosmic rays during the three consecutive solar minimum periods of 1977/1978, 1987 and 1997

Extensive data sets have been measured for galactic and anomalous cosmic rays during the past three solar minimum modulation periods of 1977, 1987, and 1997 by various spacecraft at distances ranging from 1 to 66 AU from the Sun. in this paper we investigate the radial, latitudinal, and rigidity dependence of the diffusion mean free paths (lambda) deduced from galactic helium and hydrogen in the heliosphere and compare these values with those from earlier studies by Reinecke et al. [1993, 1996] and from theoretical calculations by Zank et al. [1997, 1998].