Measurement, simulation, and meteorological interpretation of medium-range transport of radionuclides to Korea during the Fukushima Dai-ichi nuclear accident

Abstract

Two radionuclides (131I and 137Cs) were measured and simulated over the Korean Peninsula during the Fukushima Dai-ichi nuclear accident, and the resulting meso-scale meteorological characteristics were explored in order to interpret the medium-range transport of radionuclides from the site of the Fukushima Dai-ichi nuclear accident to the Korean Peninsula. Peak concentrations of radionuclides were detected across all sites in Korea for a period of April 2–8, 2011, with maximum concentrations of 131I and 137Cs at 3.12mBq/m3 (on April 6), and 1.25mBq/m3 (on April 7), respectively; the highest levels on record in Korea since measurements began. The multi-particle Lagrangian model, the FLEXPART simulation based on the National Centers for Environmental Prediction/Global Forecast System (NCEP/GFS), successfully explored these high radionuclide peaks resulting from long- and medium-range transport processes from the accident site.The meteorological feature of the medium-range transport exploited in this study is the veering meso-scale circulation, in association with the presence of a blocking anticyclone, and its subsequent evolution with propagation eastwards over northeast Asia, which was one of the important factors in explaining the advection and redirection of radionuclides from the accident site to the Korean Peninsula. The blocking situation of the anticyclone, centered on the Korean Peninsula, lasted for two days (on April 4–5, 2011), and the northwesterlies and subsequent northerlies advected the radionuclides from the accident site to the southern Sea of Japan. They were then redirected towards Korea due to the veering circulations produced by the blocking anticyclone. The position-evolution of the anticyclone was concurrent with the timing of the transport of the highest level of 137Cs concentrations recorded in Korea. The vertical meteorological structure of the blocking anticyclone was also well featured to maintain its position due to the persistent compensation provided by being aloft a convergence zone, which is in good accordance with the location of the ridge on the 500hPa level.