Neutron monitors and muon detectors for solar modulation studies: Interstellar flux, yield function, and assessment of critical parameters in count rate calculations

Abstract

Particles count rates at given Earth location and altitude result from the convolution of (i) the interstellar (IS) cosmic-ray fluxes outside the solar cavity, (ii) the time-dependent modulation of IS into Top-of-Atmosphere (TOA) fluxes, (iii) the rigidity cut-off (or geomagnetic transmission function) and grammage at the counter location, (iv) the atmosphere response to incoming TOA cosmic rays (shower development), and (v) the counter response to the various particles/energies in the shower. Count rates from neutron monitors or muon counters are therefore a proxy to solar activity. In this paper, we review all ingredients, discuss how their uncertainties impact count rate calculations, and how they translate into variation/uncertainties on the level of solar modulation $\phi$ (in the simple Force-Field approximation). The main uncertainty for neutron monitors is related to the yield function. However, many other effects have a significant impact, at the 5-10\% level on $\phi$ values. We find no clear ranking of the dominant effects, as some depend on the station position and/or the weather and/or the season. An abacus to translate any variation of count rates (for neutron and $\mu$ detectors) to a variation of the solar modulation $\phi$ is provided.

28 pages, 16 figures, 9 tables, match accepted version in AdSR (minor corrections, Dorman (1974,2004,2009) reference textbooks added)

References in corpus (6)

• Discrepant hardening observed in cosmic-ray elemental spectra
• Measurements of 0.2 to 20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer
• Historical Sunspot Observations: A Review
• Neutron Monitor Yield Function: New Improved computations
• Observations of the Li, Be, and B isotopes and constraints on cosmic-ray propagation
• p, He, and C to Fe cosmic-ray primary fluxes in diffusion models: Source and transport signatures on fluxes and ratios

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• Temporal evolution and rigidity dependence of the solar modulation lag of Galactic cosmic rays
• High-altitude polar NM with the new DAQ system as a tool to study details of the cosmic-ray induced nucleonic cascade
• Utilization of a shallow underground laboratory for studies of the energy dependent CR solar modulation