Cosmogenic ⁷Be in air: A complex mixture of production and transport

The long-time series of ⁷Be activity in surface air have been studied with the wavelet analysis technique in order to find coherence between ⁷Be activity, theoretical production in the troposphere and climatic indices. The ⁷Be activity were obtained from five different locations, Angra in the tropics in Brazil, Skåne in mid-latitudes in Southern Sweden, Kiruna in Polar region in Northern Sweden, Loviisa in Southern Finland and Rovaniemi in polar region in Northern Finland. The ⁷Be data from the Northern hemisphere sites where tested for coherence with theoretical production of the isotope in troposphere and with the North Atlantic Oscillation index. In the Southern hemisphere separate theoretical production was calculated in order to describe local production and Southern Annular Mode was used as the climatic index. Consistent and significant coherence were found with theoretical production at Skåne, Kiruna and Loviisa at time-scales of four years or longer. At Angra and Rovaniemi sites, no coherence was detected between ⁷Be theoretical tropospheric production and measured activity at ground level. The coherence between ⁷Be data from Skåne and Angra and climatic indices is insignificant while data from Northern and Eastern Scandinavia show clear coherence with climatic indices at time-scales of four years or longer. Additionally, significant coherence was found between the cosmic ray induced production and NAO at the time band of 8-12 years whereas the coherence between cosmic ray induced production and SAM was insignificant. This feature implies that the ground level ⁷Be activity contain mixed information on both production and transport. This conclusion means that further evaluation through models which enable accurate realistic models that will be investigated in future studies.