Describing the annual cyclic behaviour of Be concentrations in surface air in Oceania

Surface air concentrations of ⁷Be at a number of stations in Oceania show a distinct annual cycle. We apply a sinusoidal model to describe this cycle. The results show that peak ⁷Be concentrations in surface air occur during early spring at tropical latitudes and during mid-to-late summer at middle latitudes. Comparison with available ⁹⁰Sr surface air data for the southern hemisphere indicates that stratosphere-to-troposphere exchange is an active atmospheric process controlling the ⁷Be annual cycle throughout the Oceania region. Vertical transport of air within the troposphere also seems to influence the observed annual cycle. Seasonality in rainfall is not thought to control the annual cyclic behaviour of ⁷Be in surface air.