Influence of long term solar modulation on the relativistic muon intensity

During the period 1965 to 1971 a set of absolute muon intensity data available at stations having low vertical cut-off rigidities show a small disagreement with our latitude corrected muon intensity and this could possibly be due to the maximum increase in the Zurich sun spot number which intensifies the electric tension of earth, i.e. the Ehmert potential. The decrease of muon intensity at around 1 GeV/c during the years 1965 to 1969 is in accord with the theoretical results calculated after O'Brien when multiplied by a factor 1.085 but lies below the theoretical values calculated after Allkofer and Dau. The decrease of muon intensity is in agreement with the Deep River integral muon intensity data during the same period.