Heliocentric radial intensity profiles of galactic cosmic rays measured by the IMP, Voyager, and Pioneer spacecraft in solar 11-year modulation cycles of opposite magnetic polarity

We examine in this paper the heliocentric radial intensity profiles at heliolatitudes <35° of five energies/species of galactic cosmic rays as measured by IMP, Pioneer 10, and Voyagers 1 and 2 over several 11-year solar cycles of different solar magnetic polarity. At times of maximum solar modulation the radial profiles in each cycle are remarkably similar. At times of minimum solar modulation (maximum intensity) these radial profiles differ greatly in the negative and positive solar magnetic polarity cycles. At the positive polarity cycle intensity maximum in 1977 and 1997 these intensity profiles exhibit a strong radial dependence out to ∼15 AU, beyond which the intensity profile is nearly flat. Also in the positive polarity cycles the amplitude of the 11-year solar modulation cycle from maximum to minimum intensity decreases strongly with radius. At the negative polarity cycle intensity maximum in 1987 the radial intensity profiles at all energies are all consistent with a radial gradient which is ∼r^-0.50±0.03, which when extrapolated to 85-95 AU gives intensities a factor ∼2-3 times higher at that distance than those in the positive cycles. The maximum extrapolated intensities of H and He nuclei at 85-95 AU in the negative polarity cycle in 1987 are comparable to the estimated interstellar intensities at rigidities above ∼1.5 GV, but at rigidities below ∼1 GV they are considerably less. This suggests that additional modulation is occurring in the heliosphere beyond 85-95 AU at these times. This rigidity-dependent outer heliospheric modulation would greatly affect all particles with rigidities below a few hundred megavolts. In the positive polarity cycles, because of the lower extrapolated intensities at 85-95 AU, this outer heliospheric modulation is larger by a factor of 2-3 at all rigidities. Remarkably, in the scenario described here, a cosmic ray detector fixed at ∼85 AU in the solar ecliptic plane would probably not even see a solar 11-year variation but instead see a very asymmetrical 22-year variation which would depend on the solar magnetic polarity. Current modulation models explain some of these features when they include a heliospheric termination shock embedded in a larger modulation region.