Distribution of ~7Be in surface air of Europe

摘要

This study deals with long-term (span over three decades, 1972-2003) distribution of the cosmogenic isotope ~7Be in surface air at 5 stations in Europe, extending from latitude 47°N to 68°N. The results suggest annual variability in all the data sets as well as a decrease in average ~7Be activity with increasing latitude. Furthermore, a 9-10-year cyclical pattern is observed in the ~7Be distribution, which is anticorrelated with the solar activity cycle. Our data also indicate a dynamic range of ~7Be activity for each solar cycle and phase (maximum or minimum) which is higher at the middle compared to high-latitude regions. Additionally, about 10-20% relative deviation is observed in ~7Be activity during solar maxima and minima compared to the total average ~7Be. This feature indicates that some deviation in the worldwide ~7Be activity data may relate to their acquisition, with respect to which part of a solar cycle they have been collected in (time span) and at which latitudinal spread. Estimate of ~7Be flux onto European surface boundary layer vary from 0.4 to 0.9 x 10~(10) atomsm~(-2)yr~(-1) which is strongly latitude dependent and our average value is comparable to the ～0.7 - 0.8 x 10~(10) atoms m~(-2)yr~(-1) across ocean and land.