Sources of the seasonal-trend behaviour and periodicity modulation of 7Be air concentration in the atmospheric surface layer observed in southeastern Spain

Abstract The components and the periodicity characterising airborne 7 Be monthly concentration collected in Granada (SE Spain) between 2000 and 2018 are studied. These 19 years of measurements are particularly significant for the 7 Be analysis as they cover the complete 24th solar cycle, 2008–2018. A Time Series Decomposition (TSD) technique has been applied to determine the different components present in the dataset: the trend, seasonal and irregular components. Then, the atmospheric parameters (Precipitation (Pp), Relative Humidity (RH), Temperature (Temp), Wind speed (WS), Total Cloudiness (TC), Low Cloudiness (LC)), teleconnection indices and the solar activity (Sun Spot Number, SSN) were used to justify the variability of each component. SSN and the teleconnection indices (Western Mediterranean Oscillation (WeMO), Atlantic Multidecadal Oscillation (AMO) and Quasi Biennial Oscillation (QBO)) are found to have a major impact on the trend component of 7 Be. In turn, all the atmospheric parameters were found to have strong impact on the seasonal component. In order to observe the change in the impact of the parameters from the 24th solar cycle (from 2008 to 2018) to the complete time series (starting in 2000), the comparison between the two periods has been carried out. The results show that, over the 24th solar cycle, the SSN impacted predominantly on the trend component, whereas atmospheric parameters showed a slightly higher impact on the seasonal component. In addition, some atmospheric factors (Temp, RH, Pp, TC, LC) appeared to partially affect the irregular component. The analysis of the two phases of the 24th solar cycle shows that the influence of SSN is higher during the descending phase than during the ascending one. This behaviour is opposed to the one found for the 23rd solar cycle, which clarifies the special characteristics of the 24th cycle. Besides that, the Continuous Wavelet Transform (CWT) analysis was applied in order to extract the possible periodicities characterising 7 Be data. The analysis revealed three sets of periodicities. Then, the Wavelet Coherence Analysis (WCA) method was particularly useful to study coherences between 7 Be data and teleconnection indices. The 7 Be concentrations in the large period (11–14 years) detected by CWT was found to be mainly modulated by WeMO, AMO and QBO, while the NAO modulates the smaller periods.