Abstract
The Sun is an effective particle accelerator that produces solar energetic particle (SEP) events, during which particles of up to several GeVs can be observed. These events, when they are observed at Earth with the neutron monitor network, are called ground-level enhancements (GLEs). Although these events with their high-energy component have been investigated for several decades, a clear relation between the spectral shape of the SEPs outside the Earth’s magnetosphere and the increase in neutron monitor count rate has yet to be established. Hence, an analysis of these events is of interest for the space weather and for the solar event community.
In this article, SEP events with protons accelerated to above 500 MeV were identified using data obtained with the Electron Proton Helium Instrument (EPHIN) onboard the Solar and Heliospheric Observatory (SOHO) between 1995 and 2015. For a statistical analysis, onset times were determined for the events and the proton energy spectra were derived and fitted with a power law.
As a result, we present a list of 42 SEP events with protons accelerated to above 500 MeV measured with the EPHIN instrument onboard SOHO. The statistical analysis based on the fitted spectral slopes and absolute intensities is discussed, with special emphasis on whether an event has been observed as a GLE. Furthermore, we are able to determine that the derived intensity at 500 MeV and the observed increase in neutron monitor count rate are correlated for a subset of events.
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Acknowledgements
The SOHO/EPHIN project is supported under Grant 50 OC 1302 by the German Bundesministerium für Wirtschaft through the Deutsches Zentrum für Luft- und Raumfahrt (DLR).
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 637324.
This work was carried out within the framework of the bilateral BMBF-NRF-project ‘Astrohel’ (01DG15009) funded by the Bundesministerium für Bildung und Forschung. The responsibility of the contents of this work is with the authors.
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Kühl, P., Dresing, N., Heber, B. et al. Solar Energetic Particle Events with Protons Above 500 MeV Between 1995 and 2015 Measured with SOHO/EPHIN. Sol Phys 292, 10 (2017). https://doi.org/10.1007/s11207-016-1033-8
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DOI: https://doi.org/10.1007/s11207-016-1033-8