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Ann. Geophys., 26, 1029-1037, 2008
www.ann-geophys.net/26/1029/2008/
© European Geosciences Union 2008

Energetic particle measurements from the Ulysses/COSPIN/LET instrument obtained during the August/September 2005 events

O. E. Malandraki^1,*,**, R. G. Marsden¹, C. Tranquille¹, R. J. Forsyth², H. A. Elliott³, and A. Geranios^4
1Research and Scientific Support Department of ESA, ESTEC, Noordwijk, The Netherlands
²The Blackett Laboratory, Imperial College of Science and Technology, London, UK
³Space Science and Engineering, Southwest Research Institute, San Antonio, TX, USA
⁴Nuclear and Particle Physics Department, University of Athens, Athens, Greece
^*currently at: The Blackett Laboratory, Imperial College of Science and Technology, London, UK
^**also at: Institute for Astronomy and Astrophysics, National Observatory of Athens, Athens, Greece

Abstract. We report recent observations of energetic particles at energies 1–40 MeV/n made by the COSPIN/LET instrument onboard the Ulysses spacecraft during the period of intense solar activity in August/September 2005 during the declining phase of solar cycle 23. Ulysses, having started its climb to high southern latitudes for the third time, was located at ~5 AU, at a helio-latitude of ~30 degrees south. It detected the arrival of a solar wind compound stream resulting from the merging of a series of fast halo CMEs ejected from the Sun in late August and early September 2005 and their interaction with the pre-existing pattern of solar wind Stream Interaction Regions (SIRs) in the ambient medium through which they propagated. The heavy ion intensities are observed by COSPIN/LET to remain elevated for at least 20 days following the very intense X17.0/3B solar flare on 7 September and its associated very fast CME (plane of sky projected CME speed ~2400 km s⁻¹). We carry out an analysis of the composition of the particle increases observed at the location of the spacecraft. Although the composition signatures were predominantly Solar Energetic Particle (SEP)-like, after the passage of the compound stream over Ulysses, in association with a characteristic forward and reverse shock pair, the observations showed evidence of an enhanced He content.

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