Indications for solar influence on radon and thoron in the atmosphere, Arad, Romania

Radon (Rn-222; Rn) and Thoron (Rn-220; Tn) from the lowermost atmosphere in Arad, Romania, were investigated from 1993 to 2015. Daytime and night-time measurements exhibit (i) systematic differences; (ii) large annual variations; (iii) semi-annual and possibly ternary annual periodicities; (iv) amplitudes of the annual and semi-annual periodicities differ between daytime and night-time measurements. The day of year of the summer peak time (SPT) of the annual variation of composite Rn and Tn data depict smoothly covarying SPT patterns separated around 50 days. SPT patterns of daytime and night-time of Rn and Tn depict additional separations of gradually varying multi-year patterns. For both radionuclides, the night-time SPT precedes the daytime SPT—by around 105 days for Tn and around 60 days for Rn. In the case of temperature, the SPT of daytime and night-time measurements overlap at around day 195. Thus, for Rn and Tn, daytime and night-time differences depend on the time of measurement within the 24 h c...