The spatial distribution of galactic and anomalous cosmic rays in the heliosphere at solar minimum

The spatial distributions of galactic and anomalous cosmic rays in the heliosphere at the solar minima of Cycles 20/22 (qA > 0) and of Cycle 21 (qA < 0) are studied, using data from IMP 8, Voyagers 1/2 and Pioneer 10. It is found that the radial dependences of intensities J can be approximated by a power of radial distance r as J proportional to r(alpha) with a different value of a constant in the inner and outer heliosphere with a transition at a radial distance of 10-15 AU. To study the physical meaning of these radial intensity profiles we examined the rigidity dependences of the intensity gradients by determining the particle mean free paths, using a simple one-dimensional modulation model. The particle mean free path was assumed to be a separable function of distance of the form r(gamma) and rigidity R of R-delta over the range of 0.5-3.0 GV in the inner and outer heliosphere. It was shown that A of rigidity dependence of R-1.6 determined for Cycle 20/22 (qA > 0) with anomalous He is about 4-5 times larger than that of Cycle 21 (qA < 0) with R-0.9 at around 1 GV in the outer heliosphere, and that the radial dependences are r(1.4) and r(1.1), respectively, for Cycles 20/22 and for Cycle 21. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.