Observations of the dynamics of the cosmic ray modulation

Measurements of the galactic cosmic ray intensity for energies E > 2 GeV and E > 60 MeV near earth and for E > 60 MeV at 5 < R < 30 AU from the earth reveal the relationship of interplanetary shocks and Forbush decreases to the 11‐year cosmic ray modulation. We find that (1) during the decreasing portion of the cosmic ray intensity cycle from 1977 to 1982 the modulation is propagated outward radially from the sun with a speed of 350 < Vp < 450 km/s, (2) large rapid, transient decreases of ∼20% are seen at R ∼ 15 AU and R ∼ 28 AU in 1982, (3) the long‐term variation for E > 2 GeV during 1955–1965 and 1965–1977 can be simulated by the accumulative effects of Forbush decreases, and (4) there is a difference in the energy dependence of decrease and recovery phases of the 11‐year variation. These results clearly indicate that a time‐dependent solution to the cosmic ray transport equation is required to describe the solar cosmic ray modulation.