[M-AG38] Ten years after the Fukushima Dai-ichi NPP Accident : Dynamics of radionuclides in the environment

[MAG38-04] Comprehensive evaluation on wet scavenging schemes for ¹³⁷Cs transport modeling following the Fukushima Daiichi accident

*Shuhan Zhuang¹, sheng fang¹ (1.Tsinghua University)

Keywords:wet deposition, in-cloud scavenging, below-cloud scavenging, WRF-Chem, Fukushima Daiichi Nuclear Power Plant accident

Wet deposition, including both the in-cloud and below-cloud scavenging, is critical for the atmospheric transport modeling of ¹³⁷Cs in the Fukushima Daiichi Nuclear power plant accident. Although intensively investigated, wet deposition simulation is still subject to uncertainties of meteorological input and wet scavenging modeling, leading to biased ¹³⁷Cs transmission prediction. To solve the problems, 25 different combinations of both the in- and below-cloud scavenging schemes were integrated into the Weather Research and Forecasting-Chemistry, realizing online coupled modeling of the wet scavenging processes and meteorology. With the same emission, meteorological input and WRF settings, these 25 models and their ensemble mean were systematically compared with a previous WRF-Chem model with a single below-cloud scheme on the same platform, based on both the cumulative deposition and ambient concentration of ¹³⁷Cs following the FDNPP accident. As far as we know, this is the first evaluation of both in- and below-cloud wet scavenging schemes based on the same online-coupled model, which may provide a clearer picture of the variation range among these schemes and the capability of WRF-Chem for ¹³⁷Cs transport modeling. The results demonstrate that the integration of the in-cloud scavenging scheme substantially improves the cumulative deposition simulation in light rain dominated area like Nakadori and around FDNPP, and the in-cloud schemes contribute predominately to the detailed deposition patterns, such as those in Nakadori area, which were missing in the previous below-cloud-only WRF-Chem. However, the 25 models show diverse behaviors in the presence of different meteorology for atmospheric concentration, though the ensemble mean achieves fair and stable performance for deposition and concentration under different plume events. Specifically, only the models considering cloud parameters show potential in optimizing the overall simulation, such as the Roselle-Bakla, Hertel-Bakla and Roselle-Apsimon. In comparison, the wet deposition models dependent only on the rain intensity are very sensitive to the meteorology. So, a combination of the in-cloud scheme with cloud parameters and a below-cloud scheme using a refined power function may be promising in improving the simulation of ¹³⁷Cs.