Bremen 2017 – scientific programme

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EP: Fachverband Extraterrestrische Physik

EP 4: Sonne und Heliosphäre I

EP 4.7: Talk

Tuesday, March 14, 2017, 15:45–16:00, GW2 B2880

An empirical model to describe the modulation of galactic cosmic rays close to Earth — Jan Gieseler, •Bernd Heber, Konstantin Herbst, and Patrick Kühl — IEAP, University of Kiel, Germany

On their way through the heliosphere, Galactic Cosmic Rays (GCRs) are modulated by various effects before they can be detected at Earth. This process can be described by the Parker equation, which calculates the phase space distribution of GCRs depending on the main modulation processes: convection, drifts, diffusion and adiabatic energy changes. A first order approximation of this equation is the force field approach, reducing it to a one-parameter dependency, the solar modulation potential φ. Utilizing this approach, it is possible to reconstruct φ from ground based and spacecraft measurements. However, it has been shown previously that φ depends not only on the Local Interstellar Spectrum (LIS) but also on the energy range of interest. We have investigated this energy dependence further, using published proton intensity spectra obtained by PAMELA and SOHO/EPHIN as well as heavier nuclei measurements from IMP-8 and ACE/CRIS. Our results show severe limitations at lower energies including a strong dependence on the solar magnetic epoch. Based on these findings, we will outline a new tool to describe GCR proton spectra in the energy range from a few hundred MeV to tens of GeV over the last solar cycles.