The Relative Recovery of Galactic and Anomalous Cosmic Rays at 1 AU: Further Evidence for Modulation in the Heliosheath
F. B. McDonald1, B. Klecker2, R. E. McGuire3, and D. V. Reames3

1 IPST, University of Maryland, College Park, MD
2 Max-Planck Institut für Extraterrestrische Physik, Garching, Germany
3 NASA Goddard Space Flight Center, Greenbelt, MD

Following the passage of the large interplanetary disturbances produced by the intense solar activity of March/June 1991, it is found that over the period 1991.5-1996.2 the recovery at 1 AU of anomalous cosmic rays (ACR) is very different from that of galactic cosmic-rays (GCR). This study uses ACR oxygen data from Sampex (8-28 MeV/n) and Wind/Epact (8-18 MeV/n) and 170-380 MeV/n GCR He from Imp 8. A regression plot of 275 MeV/n He versus ACR oxygen shows that beginning in early 1994 there is approximately a 2 year period over which GCR continues to increase while there is essentially no long term change in the ACR oxygen intensity. This different recovery of the GCR and ACR components is interpreted as evidence that the heliosheath may play an important role in the longterm modulation of galactic cosmic-rays. Similar effects for this same recovery period were observed in the V-1 data (McDonald et al. 1999) near 47 AU. However the 1 AU observations do not have the complications of corrections for the radial and latitudinal intensity gradients in the outer heliosphere over this extended time period and provide a strong confirmation of the Voyager 1 results. F.B. McDonald, B. Heikkila, N. Lal and E. C. Stone, Proc. 26th ICRC, 6, 548, 1999.