Solar energetic particle propagation in 1997-99: Observations from ACE, Ulysses, and Voyagers 1 and 2

Solar energetic particles injected during intense activity in April-May 1998 and observed at ACE and Ulysses are identified in 0.5-1.5 MeV proton data from the LECP instrument on Voyager 2 (56 AU, 20 deg. S) and Voyager 1 (72 AU, 33 deg. N). A shell of ≅1 MeV protons ∼60 days wide reached peak intensity at Voyager 2 on 1998.7 and at Voyager 1 on 1998.8, some 6 months after the April-May 1998 solar activity. We interpret these results in terms of infrequent scattering during propagation from 1 to 72 AU in helioradius and over ∼50 deg. in latitude