Further indications of a ∼140 day recurrence in energetic particle fluxes at 1 and 5 AU from the Sun

Abstract

A possible ∼140 day recurrence in the fluxes and anisotropics of interplanetary MeV energy protons has previously been identified in data from the Anisotropy Telescopes (ATs) on board Ulysses. This measurement was made during 1998-1999 at a distance from the Sun of ∼5 AU. Earlier reports of a 154-day periodicity in the occurrence rate of solar flares and other solar activity indicators exist, mainly for cycle 21 data. In this paper we compare the ATs measurement, made for protons in the 1.3-2.2 MeV energy range, with fluxes of relativistic electrons (∼4-10 MeV) and protons in the range ∼30-100 MeV. We consider 5-AU data from the Ulysses Kiel Electron Telescope (KET) instrument and 1-AU measurements from the IMP 8 Cosmic Ray Nuclear Composition (CRNC) telescope. We find that at these higher energies significant fluxes at 5 AU are detected only in correspondence with a specific feature in the ATs recurrent pattern, thus supporting the hypothesis of recurrent behavior. We look for signatures of these events at 1 AU in the CRNC data and find for all of them an associated long-duration particle event, regardless of the longitudinal separation between Ulysses and IMP 8. Possible solar sources of the events are discussed. Copyright 2001 by the American Geophysical Union.