Validation of the neutron monitor yield functions using data from AMS-02 and PAMELA experiments, 2006--2017
2019 July 24
Spectra of protons and helium directly measured in space by the AMS-02 experiment for the period 2011--2017 and protons measured by the PAMELA experiment for 2006-2014 provide a unique opportunity to calibrate ground-based neutron monitors (NMs). In this work calibration of several stable sea-level NMs (Inuvik, Apatity, Oulu, Newark, Moscow, Hermanus, Athens) was performed using these measured spectra. Four modern NM yield functions were verified: Mi13 (Mishev et al., 2013), Ma16 (Mangeard et al., 2016), CM12 (Caballero-Lopez & Moraal, 2012) and CD00 (Clem & Dorman, 2000). The Mi13 yield function was found to realistically represent the NM response to galactic cosmic rays. CM12 yield function leads to a small skew in the solar cycle dependence of so-called NM scaling factors. In contrast, Ma16 and CD00 yield functions tend to overestimate the NM sensitivity to low-rigidity (<10 GV) cosmic rays. This effect may be important for an analysis of ground level enhancements (GLEs), leading to a potential underestimate of fluxes of solar energetic particles as based on data. The Mi13 yield function is recommended for quantitative analyses of NM data, especially for ground-level enhancements. The results of this work strengthen and validate the method of the cosmic-ray variability analysis based on the NM data and yield-function formalism, and improves its accuracy.