Development of three-dimensional numerical model for Rn and its decay products coupled with a mesoscale meteorological model, 2; Numerical analysis on the increase in dose rate observed in the coastal area of Fukushima prefecture

Nishizawa, Masato; Nagai, Haruyasu  ; Chino, Masamichi

A three-dimensional Eulerian numerical model for Rn and its decay products coupled with a mesoscale meteorological model, MM5-TMNR, is applied to investigate the mechanism of the naturally induced increase of dose rate observed at the coastal area of Fukushima prefecture on October, 2002. The results obtained by MM5-TMNR are verified by the comparisons with observed wind, precipitation and dose rate, and adequate to examine the mechanism. The unusual increase of dose rate is occurred by the combination of the synoptic-scale transport of natural radionuclides due to inflow of cold air mass from the Asian Continent and the meso--scale precipitation process within the coastal area of Fukushima prefecture. The contribution rate of natural radionuclides from the Asian Continent to the increase of dose rate is estimated to be more than 60%.