Modeling the long-range transport of 222Rn to subantarctic and antarctic areas

The long-range advection of 222Rn over the Indian Ocean has been studied using a three-dimensional coarse-grid (8deg x 10deg) transport model of the global troposphere based on the meteorological fields of the GWE period (December 1978-November 1979). A uniform continental source of 222Rn and a weak, wind-speed dependent oceanic source of 222Rn has been prescribed in the simulations. Model predictions are compared to observations of the 222Rn concentration at three Indian Ocean islands and one station located at the Antarctic coast. The advection of continental 222Rn to these observing sites, each being several thousand kilometers away from major landmasses, requires several days and provides a unique opportunity for the validation of the transport model on time scales ranging from a few days to the seasonal cycle induced by seasonally changing transport patterns. The model is able to simulate several features of the time series observed in the Indian Ocean; however, it fails to correctly predict the seasonal cycle and the short-term concentration variations at the Antarctic coast. (orig.)