Heliospheric modulation of cosmic rays: Monthly reconstruction for 1951–2004

The differential energy spectrum of galactic cosmic rays in the vicinity of the Earth can be parameterized by the so‐called force field model which has only one parameter, the modulation potential ϕ, for a given local interstellar spectrum. Here we present the series of monthly values of the modulation potential ϕ since February 1951, reconstructed using the data from the worldwide neutron monitor network and calibrated with precise balloon and space‐borne direct measurements of cosmic ray energy spectrum. This work provides a long series of a parameter allowing for a quantitative estimate of the average monthly differential energy spectrum of cosmic rays near the Earth. A comparison with other occasional direct measurements of cosmic ray spectra confirms the reliability of the present reconstruction. The results can be applied in studies of long‐term solar‐terrestrial relations and the global evolution of the heliosphere.