On galactic cosmic ray flux decrease near solar minima and imf intensity

We have analyzed the annual mean hourly rate data obtained with a variety of detectors located at the global sites as well as at the balloon altitudes, for the sunspot number (SSN) cycles 20, 21, 22. A systematic decrease is observed in all of them near the solar minimum epochs, for the period 1965 to 1987. The median rigidity of response (Rm) for these detectors, to the galactic cosmic ray (GCR) spectrum, lies in the range: 3GV < Rm < 67 GV. The observed decrease in GCR flux corresponds to an observed increase in the baselevel of the interplanetary magnetic field (IMF) intensity (B) during the same time period; no increase is observed in SSN minimum levels during this interval. The available data for GCR (1937 to 1998) and B (1963 to 1998) are reviewed. We argue that the cause of the observed GCR flux decrease (increase in the residual modulation) must be located in the heliosphere and not in the local interstellar medium.