REAPPEARANCE OF RECURRENT LOW-ENERGY PARTICLE EVENTS AT ULYSSES HI-SCALE IN THE NORTHERN HELIOSPHERE/

In the high-latitude northern hemisphere of the heliosphere, the Helio sphere Instrument for Spectra Composition and Anisotropy at Low Energi es (HI-SCALE) energetic particle detectors on Ulysses have measured qu asi-recurrent -26-day increases of 40-65 keV electrons during 11 solar rotations from October 1995 through July 1996. They do not appear on all rotations, but when they do, they are associated with increases in 0.5-1.0 MeV protons (preceding the electron increases by several days ) and sometimes with decreases in galactic cosmic rays. The northern r ecurrences form two series shifted half a solar rotation with respect to each other, unlike the very regular and more intense series of 21 r ecurrences observed by the same instrument throughout the middle-to-hi gh-latitude southern hemisphere from mid-1993 to the beginning of 1995 . Correlated energetic particle measurements from IMP 8 at Earth and V oyagers 1 and 2 at 42-62 AU establish that recurrent events during thi s period were intrinsically stronger in the southern heliosphere than in the north. The variability of the northern recurrences is attribute d, using a generalization of the model of Fisk [1996], to temporal cha nges during 1966 in the near-Sun polar magnetic field configuration. T hese changes would affect the connection of Ulysses via magnetic field lines to the corotating interaction regions at lower latitudes >10 AU beyond the spacecraft, where the low-energy particles are accelerated and the galactic cosmic rays are modulated. The observed evolution of the northern polar coronal structure, as revealed in FeXIV (5303 Angs trom) synoptic maps and confirmed by FeXII (195 Angstrom) images from the Extreme Ultra-Violet Imaging Telescope on the SOHO spacecraft, is just that which is required, according to the model, to explain the ev olution of the low-energy particle recurrences as observed by Ulysses/ HI-SCALE in the northern heliosphere.