Intensities of anomalous and galactic cosmic rays in the outer heliosphere near the heliospheric equator in 1987 and during the period from 1994 to 1996

Using galactic and anomalous cosmic ray data from the Pioneer 10 and Voyager 1 and 2 spacecraft in the outer heliosphere between similar to 42 and 64 AU near the heliospheric equator, we find the following comparisons between the previous intensity maximum in 1987 and the current period in 1994-1996: (1) the radial and latitudinal gradients are much smaller in 1994-1996; (2) the intensity recovery in 1994-1996 is very slow, typically only a few percent per year; and (3) the intensities in 1994-1996 are much lower than those in 1987 by a factor similar to 2 for galactic cosmic rays and similar to 6 for anomalous cosmic rays. These features all combine to suggest that in 1997 at the probable time of the next sunspot minimum the intensities of both galactic and anomalous cosmic rays will be much lower than they were in the previous cycle in the outer heliosphere at 42 AU and beyond, including the location of a possible termination shock in the range 70-85 AU. We attribute these intensity differences between Ii-year cycles to drift effects near the termination shock. These effects reduce the galactic cosmic ray spectrum near the equator at low energies in 1996 relative to 1987, producing a barrier-like reduction of intensity across the shock region at this time, while at the same time the intensity just inside the shock near the poles may be much higher in 1996 than in 1987. This effect gives rise to a 22-year modulation wave that is strongest in the outer heliosphere near the shock but has important effects near the Earth as well.