The radial distribution of cosmic rays in the heliosphere at solar maximum

Abstract To obtain a more detailed profile of the radial distribution of galactic (GCRs) and anomalous (ACRs) cosmic rays, a unique time in the 11-year solar activity cycle has been selected - that of solar maximum. At this time of minimum cosmic ray intensity a simple, straight-forward normalization technique has been found that allows the cosmic ray data from IMP 8, Pioneer 10 (P-10) and Voyagers 1 and 2 (V1, V2) to be combined for the solar maxima of cycles 21, 22 and 23. This combined distribution reveals a functional form of the radial gradient that varies as G 0 /r with G 0 being constant and relatively small in the inner heliosphere. After a transition region between ∼10 and 20 AU, G 0 increases to a much larger value that remains constant between ∼25 and 82 AU. This implies that at solar maximum the changes that produce the 11-year modulation cycle are mainly occurring in the outer heliosphere between ∼15 AU and the termination shock. These observations are not inconsistent with the concept that Global Merged Interaction. regions (GMIRs) are the principal agent of modulation between solar minimum and solar maximum. There does not appear to be a significant change in the amount of heliosheath modulation occurring between the 1997 solar minimum and the cycle 23 solar maximum.