Development of Three-Dimensional Numerical Model for 222Rn and its Decay Products Coupled with a Mesoscale Meteorological Model I. Model Description and Validation

A three-dimensional Eulerian numerical model for 222Rn and its decay products coupled with a mesoscale meteorological model has been developed and applied to the reproduction of the daily and monthly variations of 222Rn concentration, the monthly variation of 210Pb deposition in Japan and the temporal variation of gamma dose rate after the cold front passage in the coastal area of the Japan Sea for the verification of model capability. The results are as follows: (1) The model reproduced the monthly variation of surface 222Rn concentration in remote islands, but underestimated inland concentration due to a coarse vertical resolution near the surface of the model. (2) The model reproduced the seasonal variation of the observed and the long-term yearly averaged 210Pb depositions as long as precipitations are predicted precisely. (3) The model reproduced the rise of gamma dose rate in precipitation accompanied by the cold front passage. In particular, 222Rn decay products in melted snow and graupel contribut...