Abstract
The solar modulation of galactic cosmic rays (GCR) can be studied in detail by examining long-term variations of the GCR energy spectrum (e.g. on the scales of a solar cycle). With almost 20 years of data, the Electron Proton Helium INstrument (EPHIN) onboard the SOlar and Heliospheric Observatory (SOHO) is well suited for this kind of investigation. Although the design of the instrument is optimised to measure proton and helium isotope spectra up to \(50~\mbox{MeV}\,\mbox{nucleon}^{-1}\), the capability exists to determine proton energy spectra from 250 MeV up to above 1.6 GeV. Therefore we developed a sophisticated inversion method to calculate such proton spectra. The method relies on a GEANT4 Monte Carlo simulation of the instrument and a simplified spacecraft model that calculates the energy-response function of EPHIN for electrons, protons, and heavier ions. For validation purposes, proton spectra based on this method are compared to various balloon missions and space instrumentation. As a result we present annual galactic cosmic-ray spectra from 1995 to 2014.
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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). SOHO is a project of international cooperation between ESA and NASA.
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.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 637324.
Raúl Gómez-Herrero acknowledges the financial support by the Spanish MINECO under projects ESP2013-48346-C2-1-R and AYA2012-39810-C02-01.
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Kühl, P., Gómez-Herrero, R. & Heber, B. Annual Cosmic Ray Spectra from 250 MeV up to 1.6 GeV from 1995 – 2014 Measured with the Electron Proton Helium Instrument onboard SOHO. Sol Phys 291, 965–974 (2016). https://doi.org/10.1007/s11207-016-0879-0
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DOI: https://doi.org/10.1007/s11207-016-0879-0