A COMPARATIVE-STUDY OF COSMIC-RAY RADIAL AND LATITUDINAL GRADIENTS INTHE INNER AND OUTER HELIOSPHERE

The radial and latitudinal intensity gradients of 145-255 MeV/nucleon He, 34-50 MeV/nucleon He and 30-69 MeV H are studied over an extensive range of heliocentric distances and latitudes for the 1993.0-1996.0 t ime period using data from cosmic ray experiments on the Ulysses, IMP 8, Voyager 1 and 2, and Pioneer 10 spacecraft. The radial gradients ar e found to decrease rapidly with increasing heliocentric distance and agree with those measured 20 years earlier at a similar phase of the h eliomagnetic cycle. The latitudinal gradients measured in the inner an d outer heliosphere are in reasonable agreement and positive albeit ex ceedingly small. In agreement with other Ulysses energetic particle ex periments it is found that a shift of heliolatitude by -7 degrees to - 10 degrees is necessary to get reasonable symmetry in the measurements at midlatitudes. From the Ulysses data it appears there is a signific antly reduced latitudinal variation in the intensity of the three ener getic particle components at (magnetic) heliolatitudes above about 50 degrees at this phase of the modulation cycle. Such a reduced entry of cosmic rays over such an extensive area above the solar poles implies a strong modification of the previously assumed cosmic ray transport processes at high latitudes, most probably a considerably increased ra te of scattering combined with reduced particle gradient and curvature drifts. A significant higher intensity is observed over the north sol ar pole than over the south pole for the low-energy components after t he corrections have been applied for the temporal changes at the 1-AU baseline.