Analysis of trends, periodicities, and correlations in the beryllium-7 time series in Northern Europe. (June 2019)

• Record Type: Journal Article
• Authors: Bianchi, Stefano; Plastino, Wolfango; Brattich, Erika; Djurdjevic, Vladimir; Longo, Alessandro; Hernández-Ceballos, Miguel A.; Sarvan, Darko; Ajtić, Jelena
• Is Part Of: Applied radiation and isotopes. Volume 148(2019:Jun.)
• Page Start: 160
• Page End: 167
• Publication Date: 2019-06
• Subjects: Beryllium-7 -- Decomposition -- Outliers -- Hurst exponent -- Cross-correlation; Radiology -- Periodicals; Radiation -- Industrial applications -- Periodicals; Nuclear chemistry -- Periodicals; Internet resource; Periodical; 660.298
• DOI: 10.1016/j.apradiso.2019.03.038
• Languages: English
• ISSNs: 0969-8043

Abstract

Abstract: The activity concentrations of beryllium-7, a natural radiotracer that is considered as a tracer of the stratospheric-tropospheric exchange, shows a distinct behaviour in Northern Europe compared to the central and southern parts of the continent. In this study, we use the measurements collected at four sampling stations in Scandinavia (Ivalo, Umea, Kista, Risoe) between 2001 and 2010 and investigate their trends, periodicities and residuals with the aim to further understand the common features in the beryllium-7 data records in northern sampling sites. The beryllium-7 activity concentrations exhibit statistically significant positive trends that range from an average value of 1.50%/year to an average value of 2.96%/year. We detect a one-year periodicity in all the sites, and in the southernmost site, Risoe in Denmark, additional higher-frequency harmonics. In the residual time series, we find outliers that represent occurrences of extremely high beryllium-7 activity concentration. Cross-correlations of the beryllium-7 residuals across the four sites decrease with increasing distance; similarly, as indicated by local Hurst exponents the records exhibit long-range correlations that weaken towards the end of the investigated period. To investigate the causes of the detected trends, we also calculate correlations between beryllium-7 and factors related to its production, transport and removal from the atmosphere: in particular, cross-correlations of the beryllium-7 residuals with residuals in sunspot number, local temperature, atmospheric pressure and precipitation, as well as Arctic Oscillation index and North Atlantic Oscillation index. Most of the obtained correlations, however, are not statistically significant, highlighting the need to analyse a longer time period in order to evaluate the impact of different factors on the airborne beryllium-7 activity concentration. Highlights: 7 Be records over 2001–2010 show statistically significant positive trends. Only in Risoe, shorter 7 Be periodicities are superimposed on the seasonal cycle. 7 Be cross-correlations across the sites decrease with the increasing distance. 7 Be long-range correlations evident early in the investigated years.