Seasonal variations of diurnal variations of CR muon flux

Abstract

Cosmic-ray muon flux is continuously measured in descending phase of solar cycle 23 at ground level and at the depth of 25 m.w.e. in Belgrade (20o23′E and 44o51′N). Diurnal and semidiurnal variations are present in both data sets. The mean amplitude of diurnal variation for the investigated period is 1.96(7) × 10-3 for ground level data and 9(1)×10-4 for underground data. Both diurnal and semidiurnal variations of the ground data exhibit significant seasonal variations, with amplitude maxima near solstices, while such variations are absent from the underground data within statistical uncertainty.