An empirical modification of the force field approach to describe the modulation of galactic cosmic rays close to Earth in a broad range of rigidities

Abstract

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 $\varphi$. Utilizing this approach, it is possible to reconstruct $\varphi$ from ground based and spacecraft measurements. However, it has been shown previously that $\varphi$ 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 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. In order to show the importance of our modification, we calculate the global production rates of the cosmogenic radionuclide ${}^{10}$Be which is a proxy for the solar activity ranging back thousands of years.

References in corpus (6)

• The cosmic-ray electron flux measured by the PAMELA experiment between 1 and 625 GeV
• Measurements of 0.2 to 20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer
• Heliospheric modulation of cosmic rays during the neutron monitor era: Calibration using PAMELA data for 2006--2010
• Neutron Monitor Yield Function: New Improved computations
• Solar Energetic Particle Events with Protons above 500 MeV between 1995 and 2015 Measured with SOHO/EPHIN
• Pitch-angle scattering of energetic particles with adiabatic focusing

Cited by in corpus (5)

• Validation of the neutron monitor yield function using data from AMS-02 experiment, 2011--2017
• Testing diffusion of cosmic rays in the heliosphere with proton and helium data from AMS
• Numerical modeling of cosmic-ray transport in the heliosphere and interpretation of the proton-to-helium ratio in Solar Cycle 24
• Evolution of coronal mass ejections and the corresponding Forbush decreases: modelling vs multi-spacecraft observations
• Current sheets, plasmoids and flux ropes in the heliosphere. Part II: Theoretical aspects