Energetic particle observations by Ulysses during the declining phase of solar cycle 23

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Read Full Article (file size: 631369 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A06111, doi:10.1029/2006JA011876, 2007 Energetic particle observations by Ulysses during the declining phase of solar cycle 23 O. E. Malandraki Research and Scientific Support Department of ESA, ESTEC, Noordwijk, Netherlands R. G. Marsden Research and Scientific Support Department of ESA, ESTEC, Noordwijk, Netherlands C. Tranquille Research and Scientific Support Department of ESA, ESTEC, Noordwijk, Netherlands R. J. Forsyth The Blackett Laboratory, Imperial College of Science and Technology, London, England H. A. Elliott Space Science and Engineering, Southwest Research Institute, San Antonio, Texas, USA L. J. Lanzerotti Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, New Jersey, USA Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey, USA A. Geranios Nuclear and Physics Department, University of Athens, Athens, Greece Abstract We present recent energetic particle measurements from 1–20 MeV/n recorded by the Ulysses/COSPIN/LET instrument from mid-October to the end of November 2003 and from May 2004 to the end of February 2005. Long-lasting periods with enhanced solar activity occurred during the declining phase of the current solar cycle contributing to the high-intensity particle events and heavy ion signatures observed by Ulysses near the ecliptic plane, at ∼5 AU from the Sun. The energetic particles injected from the Sun during the January 2005 intense solar activity were not observed at Ulysses until a stream interface that acted as a barrier for the particles reached the spacecraft. Our observations during this period thus show that the propagation of energetic particles is largely governed by the existence of large-scale solar wind structures that impede the transport of the particles. We use the elemental composition of the particle fluxes recorded by COSPIN/LET to gain insight into the possible origin of the particle events. We study and provide a possible interpretation of the composition signatures observed at ∼5 AU during periods of CME/CIR combinations. Although predominantly SEP-like, the observed composition showed evidence for enhancements in He, which we suggest is of interstellar origin, consistent with CIR shocks accelerating ions from multiple sources. Received 26 May 2006; accepted 1 February 2007; published 21 June 2007. Keywords: Energetic particles. Index Terms: 2114 Interplanetary Physics: Energetic particles (7514); 2104 Interplanetary Physics: Cosmic rays; 2102 Interplanetary Physics: Corotating streams; 2134 Interplanetary Physics: Interplanetary magnetic fields. Read Full Article (file size: 631369 bytes) Cited by Citation: Malandraki, O. E., R. G. Marsden, C. Tranquille, R. J. Forsyth, H. A. Elliott, L. J. Lanzerotti, and A. Geranios (2007), Energetic particle observations by Ulysses during the declining phase of solar cycle 23, J. Geophys. Res., 112, A06111, doi:10.1029/2006JA011876. Copyright 2007 by the American Geophysical Union.

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