Annual Cosmic Ray Spectra from 250 MeV up to 1.6 GeV from 1995 - 2014 Measured With the Electron Proton Helium Instrument onboard SOHO

TL;DR

This study analyzes 20 years of data from the SOHO spacecraft's EPHIN instrument to produce annual cosmic ray spectra from 250 MeV to 1.6 GeV, revealing long-term solar modulation effects.

Contribution

Developed a novel inversion method using GEANT4 simulations to extract high-energy proton spectra from EPHIN data, extending its capabilities beyond original design.

Findings

Annual GCR spectra from 1995 to 2014 presented

Method validated against balloon and space data

Long-term variations linked to solar activity

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 optimized to measure proton and helium isotope spectra up to 50 MeV 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.