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Published August 2014 | public
Journal Article

> 25 MeV Proton Events Observed by the High Energy Telescopes on the STEREO A and B Spacecraft and/or at Earth During the First ~ Seven Years of the STEREO Mission


Using observations from the High Energy Telescopes (HETs) on the STEREO A and B spacecraft and similar observations from near-Earth spacecraft, we summarize the properties of more than 200 individual > 25 MeV solar proton events, some detected by multiple spacecraft, that occurred from the beginning of the STEREO mission in October 2006 to December 2013, and provide a catalog of these events and their solar sources and associations. Longitudinal dependencies of the electron and proton peak intensities and delays to onset and peak intensity relative to the solar event have been examined for 25 three-spacecraft particle events. Expressed as Gaussians, peak intensities fall off with longitude with σ=47±14∘ for 0.7 – 4 MeV electrons, and σ=43±13∘ for 14 – 24 MeV protons. Several particle events are discussed in more detail, including one on 3 November 2011, in which ∼ 25 MeV protons filled the inner heliosphere within 90 minutes of the solar event, and another on 7 March 2012, in which we demonstrate that the first of two coronal mass ejections that erupted from an active region within ∼ 1 hour was associated with particle acceleration. Comparing the current Solar Cycle 24 with the previous cycle, the first > 25 MeV proton event was detected at Earth in the current solar cycle around one year after smoothed sunspot minimum, compared with a delay of only two months in Cycle 23. Otherwise, solar energetic particle event occurrence rates were reasonably similar during the rising phases of Cycles 23 and 24. However, the rate declined in 2013, reflecting the decline in sunspot number since the peak in the northern-hemisphere sunspot number in November 2011. Observations in late 2013 suggest that the rate may be rising again in association with an increase in the southern sunspot number.

Additional Information

© 2014 Springer Science+Business Media Dordrecht. Received: 27 September 2013; Accepted: 27 March 2014; Published online: 15 April 2014. We thank Janet Luhmann of the University of California, Berkeley, for her steadfast support as the Principal Investigator of the STEREO/IMPACT investigation. The work at GSFC, Caltech and JPL was supported by NASA (Caltech and JPL were funded under subcontract SA2715-26309 from the University of California, Berkeley, under NASA Contract NAS5-03131). The LASCO CME catalog at http://cdaw.gsfc.nasa.gov/CME_list/ is generated and maintained at the CDAW Data Center by NASA and The Catholic University of America in cooperation with the Naval Research Laboratory. We particularly appreciate the efforts by S. Yashiro and colleagues to generate daily summary movies of SOHO and STEREO observations (http://cdaw.gsfc.nasa.gov/stereo/daily_movies/), which were very helpful in verifying the solar sources of the SEP events. The CACTUS CME catalog is maintained by the Solar Influences Data Analysis Center at the Royal Observatory of Belgium. The SOHO/ERNE data were obtained from the Space Research Laboratory, University of Turku (http://www.srl.utu.fi/erne_data/). The SOHO/EPHIN project is supported under grant No. 50 OC 1302 by the German Bundesminister für Wirtschaft through the Deutsches Zentrum für Luft- und Raumfahrt (DLR). SOHO is a project of international cooperation between ESA and NASA.

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