The Onset of Solar Modulation of Anomalous Cosmic-Rays in the Outer Heliosphere
A. C. Cummings and E. C. Stone
Space Radiation Laboratory
Caltech, Pasadena, CA 91125, USA

By the time of the symposium, Voyagers 1 and 2 (V1 and V2) will be approximately 76 and 60 AU from the Sun, respectively. We have been tracking the intensity of anomalous cosmic-ray (ACR) oxygen with 7.1-17.1 MeV/nuc on both Voyagers and comparing their time histores to predictions of a ``tilt'' model of modulation. This model suggests that the intensity of ACR oxygen at V2 should decrease by a factor of about 2 from beginning to end of 1999, if the solar wind termination shock is stationary at about 85 AU from the Sun. The intensity decrease at V1 should be only about 15%. Up to mid-1999, the ACR O intensities at V1 and V2 have been very stable, neither showing any significant long-term decrease. We will examine the most recent Voyager data to check if the tilt model parameters that fit the 1977-1998 data rather well are still valid, or whether, for example, the shock location needs to be moved inwards. This work was supported by NASA under contract NAS7-918.