Revised Reconstruction of the Heliospheric Modulation Potential for 1964–2022

Abstract

AbstractGalactic cosmic rays (GCRs) impinge on the Earth's atmosphere and generate showers of secondary particles in nuclear collisions with the atmospheric constituents. The flux of GCR near Earth is subjected to heliospheric modulation driven by solar magnetic activity and to geomagnetic shielding. Variability of the GCR flux is continuously monitored by the worldwide network of ground‐based neutron monitors (NMs) since the 1950s. Solar modulation is often quantified via the force‐field approximation parameterized by the modulation potential ϕ, which can be evaluated from the global NM data set. Here we revisit the methodology and provide an updated and extended reconstruction of the heliospheric modulation potential for 1964–2022, using a recent NM yield function and the measurements of the 10 most stable high‐latitude NMs. A key improvement in the reconstructed heliospheric modulation potential is the new daily resolution, which provides new opportunities for further research. Reconstruction uses the root‐mean square error (RMSE) minimization to find the optimum daily and monthly scaling factors for individual NMs. The stability of the reconstruction is analyzed and the errors are estimated. The mean level of uncertainty is low, generally within ±1%, but it is found to depict marginal variability at the 11‐year, annual and 27‐day timescales at the <1% level, indicating that a very small systematic uncertainty is still present.