Heliospheric modulation of galactic cosmic rays: Effective energy of ground-based detectors

Variability of Galactic cosmic ray (GCR) is often expressed in terms of the modulation potential, which is typically assessed using energy-integrating ground-based detectors, such as neutron monitors (NMs) for the last decades or cosmogenic isotopes on the time scales of centuries and millennia. In order to estimate the energy dependence of the GCR variability we re-assess here the effective energy Eeff of each type of detector, which is defined so that the variability of the GCR particles at this energy is equal to that of the detector's count rate. We found that Eeff is 11-12 GeV/nuc for the standard polar sea-level neutron monitor, but it is essentially smaller for cosmogenic isotopes, being 6-7 GeV/nuc for 14C and 5.5-6 GeV/nuc for 10Be, respectively. It is also discussed that this effective energy is robustly defined and is hardly dependent on the primary assumptions on the local interstellar spectrum (LIS) of GCR. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International License (CC BY-NC-ND 4.0).