Time series study of a 17-year record of 7Be and 210Pb fluxes in northern Taiwan using ensemble empirical mode decomposition

•Using EEMD method to study the time series of 7Be and 210Pb.•The results provide probable factors controlling 7Be and 210Pb including monsoon delivery, deposition and solar modulation.•We also discussed the probable factors controlling abnormal 210Pb fluxes by analyzing dust records.

Using the ensemble empirical mode decomposition (EEMD) and a significance test method, we have analyzed time series data on the fluxes of 7Be and 210Pb collected over a span of 17 y in Northern Taiwan. Among nine intrinsic mode functions (IMFs) extracted from the method five (IMF4–8) are non-trivial for 210Pb and have adequate S/N with significant power in localized windows around the periodicities of 0.5 y, 1 y, 2 y, 5 y, and 11 y, respectively. For 7Be, IMF5 and IMF8 with periods around 1 y and 11 y, respectively, have adequate S/N. The semi-annual and annual cycles represented by IMF4 and IMF5, respectively, are dominated by East Asian monsoon. The sum of IMF6 and IMF7 reveals an inter-annual cycle where both 7Be and 210Pb fluxes are well-correlated with the East Asian winter monsoon index (EAWMI). The close tracking of the 210Pb and 7Be in IMF8 cases may reflect an 11 y cycle; implying that it is caused by common climatologic factors, likely related to solar cycle, rather than their distinct production modes.