Studies of the cosmic ray radial and latitudinal intensity gradients over the cycle 22 solar minimum period

Abstract

The spatial intensity gradients of galactic and anomalous cosmic ray helium are studied over the 1993.0–1998.0 time period using data from cosmic ray experiments on IMP 8, Ulysses, Voyagers 1 and 2 and Pioneer 10. When combined with the results of previous studies, a remarkable ordering of the radial gradients for the galactic component is found over 2 complete solar cycles and 3 successive solar minima. The latitudinal gradients for the cycle 22 solar minimum period are zero or small and positive in the inner and outer heliosphere in contrast to the much larger negative latitudinal gradients observed in the outer heliosphere in 1987 over the cycle 21 solar minimum. The changes in the intensity gradients over the 3 solar minimum periods require that at these times drift effects play an important role in the transport of cosmic rays in the heliosphere and provide further evidence for the existence of a 22-year solar modulation cycle. The Ulysses data plays a pivotal role in understanding the spatial gradients over the cycle 22 recovery and solar minimum period.