AN OBSERVATION OF A HELIOSPHERIC MAGNETIC CYCLE DEPENDENCE FOR THE INTEGRAL RADIAL GRADIENT OF E-GREATER-THAN-60 MEV COSMIC-RAYS

We find that the magnitudes of the integral radial gradients of > 60 MeV cosmic ray particles as measured between Pioneer 10 (P10) and IMP and between Voyager 2 (V2) and IMP (also P10 and V2) during a period of negative solar magnetic polarity are a strong function of the cosmic ray intensity. These gradients increase from approximately 1.5%/AU at the time of peak intensity in 1987 to approximately 3%/AU at the times of minimum intensity in 1982 and 1990. During this time a strong radial dependence of the differential radial gradient was also observed, correlated with the appearance of a latitudinal gradient as measured between V2 and V1. In an earlier period of positive polarity from 1977 to 1982 we found practically no dependence of the magnitude of the integral radial gradient on the cosmic ray intensity. This gradient remained at approximately 3%/AU during the entire period and no significant radial dependence of the differential gradient was observed. These specific changes in the behavior of the gradient in opposite polarity cycles do not seem to be predicted by either the drift-wavy current sheet or simple diffusion-convection models of the solar modulation, although it is interesting to note that the dependence of the magnitude of the radial gradient on intensity observed during the negative polarity period from 1982 to 1990 is consistent with the predictions of simple diffusion-convection models. These results are discussed in the context of our understanding of the causes for the asymmetry in the 11-year modulation cycles, particularly with regard to how particles enter the heliosphere and how, once inside the heliosphere, they move from the polar to the equatorial regions.