engleski

Solar activity cycles recorded in long-term data on tritium activity concentration in precipitation at Zagreb, Croatia

Radioactive isotope of hydrogen, tritium (3H), with the half-life of 12.32 years, is of both cosmogenic and anthropogenic origin. As a part of tritiated water, H3HO, it enters the natural water cycle. Massive injections of anthropogenic 3H from weapons tests in the 1950s and 1960s caused an almost 1000-fold increase in the tritium activity concentration in precipitation, known as the “bomb peak”. After the cessation of atmospheric nuclear weapons tests, a gradual decrease in 3H activity concentration in precipitation was observed worldwide approaching presently the natural pre-bomb level. Monitoring of tritium activity concentration in monthly precipitation at Zagreb (Croatia) has been continuously performed since 1976. Seasonal variations were superposed on the basic decreasing trend of mean annual values until approximately 1996. Between 1996 and 2019 no significant decrease has been observed, while seasonal variations remained observable, with winter activities close to the natural pre-bomb 3H activity concentrations. Tritium has been widely used for studying time scale of hydrologic processes in the last decades of the 20th century. Its present scientific value for hydrological applications has significantly declined. On the other side, prevailing anthropogenic tritium in precipitation before 1996 prevented studies on whether the natural production of (cosmogenic) tritium was influenced by variations in solar activities. Our long-term data were evaluated by applying frequency analysis together with wavelet analysis. Both mathematical methods gave strong evidence of the correlation of tritium variation in precipitation with the 11-year solar cycle and so neutron flux. These findings support evidence of solar influence on meteoric tritium.

tritium ; precipitation ; Zagreb ; frequency analysis ; wavelet ; sinusoidal fit ; solar activity

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