基于WRF-Chem模式的放射性核素多元变量参数化和初始场同化研究

核爆炸或核泄漏产生的放射性核素通常以气溶胶和气态污染物的形式传播，在大气环流的作用下会造成大范围的核污染，严重危害人类健康和自然环境。由于核素传播过程物理化学机制的复杂性，以及资料同化应用的不足，目前区域尺度核素扩散预报的准确率比较低。本项目将利用WRF-Chem大气化学耦合模式，发展氙、碘、铯等多种典型放射性核素的参数化方案，考虑核素的不同相态和粒径段变量，建立多元核素变量的衰变、干沉降、湿沉降等物理化学模块，实现对多元核素的精细化预报。在此基础上，估计WRF-Chem模式多元核素变量的背景误差协方差，设计核素比活度、沉降率、剂量率等多源资料的观测算子，建立核素初始场的变分同化系统，并利用日本福岛核事故资料开展同化和预报试验研究。通过本项目的研究，将深化对核素的传播机制及其模式参数化的理解，提高核素初始场的分析质量及短期预报的准确率，为区域核污染的应急响应提供理论和技术支撑。

Radionuclides released by nuclear explosion or leakage are usually transported in the form of aerosol or gaseous pollutants. It may cause a wide range of radioactive contamination under the influence of atmospheric circulation, which is a great threat to human health and the environment. Due to the complexity of the physical and chemical mechanism of radionuclides, and the inadequacy of data assimilation, the forecasting accuracy of regional-scale radionuclide dispersion is relatively low. To improve the forecasting accuracy, it is necessary to develop the atmospheric chemical coupling model based on Euler coordinates. In this study, by using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), we will develop a new parameterization scheme with multiple radionuclides, such as 133Xe, 131I, 137Cs. Meanwhile, the multivariate variables with different phases and particle size distribution of these radionuclides are considered in the parameterization scheme. The physical and chemical modules such as the decay of nuclides and dry/wet deposition, are established for these multivariate variables. After these new improvements, the WRF-Chem can forecast precisely multiple radionuclides. Based on the results of the WRF-Chem, background error covariances of multivariate radionuclide variables will be estimated, and the observation operator for the activity concentration, deposition velocity and dose rate will be designed. Then, the data assimilation system for the initial field of multiple radionuclides will be developed. The established data assimilation and forecast system will be validated by the Fukushima Daiichi Nuclear Power Station accident. Through this study, it is expected to understand deeply the transport mechanism and the model parameterization of the multiple radionuclides in air dispersion models, and to improve the analysis quality of the initial field and the accuracy of the short-term forecast of radionuclides. In addition, this study will provide theoretical and technical support for the emergency response of the regional radioactive pollution.