Step decreases observed at 1 AU and in the distant heliosphere: 1997 – 2002 Original Research Article

The period 1997 – 2002, spans the time from the solar minimum of cycle 22 through that of solar maximum for cycle 23. At 1 AU the intensity of 265 MeV/n galactic cosmic rays (GCR) He decreased by a factor of 5.06 ± 0.07 over this period through a series of some 5 step decreases. At this time Voyagers 1 and 2 were moving between 50 and 84 AU. These modulation features are convected out to the distant heliosphere but the step size for GCR He and H is much smaller than that observed at 1 AU. At 80 AU the intensity of GCR He decreased by a factor of 1.28 ± 0.02 from, solar minimum to solar maximum. For the lower rigidity cosmic rays the modulation features are similar to those at 1 AU except that the magnitude of the step decreases are much smaller. In this study we compare the 1 AU step decreases with those in the distant heliosphere as a function of particle rigidity. The solar activity that may be producing these decreases is also investigated.