Neutron Monitors and Cosmogenic Isotopes as Cosmic Ray Energy‐Integration Detectors: Effective Yield Functions, Effective Energy, and Its Dependence on the Local Interstellar Spectrum

Abstract

The method of assessment of galactic cosmic rays (GCR) variability over different timescales, using energy‐integrating ground‐based detectors such as a neutron monitor and cosmogenic isotopes 10Be and 14C stored in natural archives is revisited here. The effective yield functions for cosmogenic 14C (globally mixed in the atmosphere) and 10Be (realistically deposited in the polar region) are calculated and provided, in a tabulated form, in the supporting information. The effective energy of a detector is redefined so that the variability of the flux of GCR particles at this energy is equal to that of the detector's count rate. The effective energy is found as 11–12 GeV/nucleon for the standard polar neutron monitor, and 6–7 GeV/nucleon and 5.5–6 GeV/nucleon for 14C and 10Be, respectively. New “calibration” relations between the force‐field modulation potentials, based on different models of local interstellar spectra (LIS) are provided. While such relations are typically based on refitting the modeled cosmic ray spectra with a prescribed LIS model, the method introduced here straightforwardly accounts for the exact type of the detector used to assess the spectrum. The relations are given separately for ground‐based neutron monitors and cosmogenic isotopes. This work allows for harmonization of different works related to variability of galactic cosmic ray flux in the vicinity of Earth, on long‐term scale.

Features of the Galactic Cosmic Ray Anisotropy in Solar Cycle 24 and Solar Minima 23/24 and 24/25

“…Unfortunately the above-mentioned effective energy concepts are not constant but are changing through the solar activity cycle. Recently, Gil et al (2017) proposed a model of the effective energy in which the variability of the GCR flux at this energy is directly proportional to the detector's count rate, so that the percentage variability of the detector's count rate is equal to that of the GCR flux at this energy; for details see Asvestari et al (2017).…”

“…In this paper we compare the analysis of the GCR anisotropy using this two approaches: the median rigidity R m of NM response (Ahluwalia et al, 2015;Ahluwalia and Fikani, 2007) and the effective rigidity R ef characteristic for each NM proposed by (Gil et al, 2017;Asvestari et al, 2017).…”

Validation of the Neutron Monitor Yield Function Using Data From AMS‐02 Experiment, 2011–2017

“…AMS is a high‐precision magnetic spectrometer installed on the International Space Station in May 2011, capable of measuring GCR fluxes in the rigidity range from 1 GV to 3 TV with uncertainties well below 10% (Aguilar et al, ). The low orbit of International Space Station is inside the Earth's magnetosphere, but thanks to its significant inclination of ≈52° to the equator, it allows one to measure particles with rigidity as low as ≈1 GV, which is sufficient for the present study, since the relative contribution of <1‐GV particles to the count rate of a polar NM is less than 10 −4 (Asvestari et al, ). We used the proton and helium spectra (Aguilar et al, ) measured from May 2011 through May 2017 for 79 BRs 2426–2506 (BRs 2472 and 2473 are missing in the data) as available at the National Aeronautics and Space Administration (NASA) Space Physics Data Facility (SPDF) Database (see Acknowledgments section).…”

Effective Rigidity of a Polar Neutron Monitor for Recording Ground-Level Enhancements

“…However, these approaches are very inaccurate, since the median energy varies over the solar cycle and thus cannot be a parameter of the detector itself. As an alternative, the concept of the "effective" energy of a NM to detect GCR has been introduced by Alanko et al (2003) and further developed by Asvestari et al (2017b). It is defined as the energy at which the variability of GCR is proportional to the recorded NM count rates.…”