基于WRF-Chem模式气溶胶多物种多粒径段组合变量的卫星AOD直接同化技术研究

Modeling and forecasting based on atmospheric chemistry model has become an important ways to effectively deal with aerosol pollution such as PM2.5 and PM10. Data assimilation can improve the initial field of atmospheric chemistry model by integrating the observed data, so as to improve the accuracy of the model prediction. Because of its wide coverage and high resolution, satellite AOD data is the most important source of aerosol data assimilation. However, due to the complex non-linear relationship among satellite AOD and aerosol species (chemical composition), particle size distribution and relative humidity, it is difficult to directly assimilate. This project will focus on developing direct assimilation of satellite AODs based on the multi-species and multi-particle size bins of the MOSAIC aerosol program in the WRF-Chem model. Then, aerosol variables are optimally combined based on the aerosol optical properties, horizontal and vertical correlations to construct background error covariance. Developing Complex AOD observation operator and its adjoint operator based on the Mie theory. An efficient satellite AOD data assimilation system was developed and validated by numerical experiments. The system will provide theoretical and technical support for improving aerosol simulation and forecasting.

基于大气化学模式的分析预报已成为有效应对PM2.5、PM10等气溶胶污染重要的手段之一。资料同化通过融合观测资料，能够有效改进大气化学模式的初始场，提高模式预报的准确性。卫星AOD资料由于覆盖面广、分辨率高，是气溶胶资料同化最重要的资料源，但由于卫星AOD与气溶胶的物种（化学成分）、粒径分布以及相对湿度之间存在复杂的非线性关系，难以直接进行同化。本项目将基于WRF-Chem模式中MOSAIC气溶胶方案的多物种和多粒径段变量，研究卫星AOD的直接同化方法；根据气溶胶光学特性、水平和垂直相关特征对气溶胶变量进行优化组合，设计区分物种及粒径大小的背景误差协方差，基于米散射理论构建复杂的AOD观测算子及其伴随算子；建立一个准确、高效的卫星AOD资料直接同化系统，并通过数值试验验证同化系统的合理性和可靠性，为提高气溶胶模拟和预报水平提供理论和技术支撑。

基于新一代大气化学耦合模式WRF-Chem中MOSAIC气溶胶方案的多物种和多粒径段变量，设计区分物种及粒径大小的背景误差协方差，基于米散射理论构建复杂的AOD观测算子及其伴随算子，建立了区分物种和粒径段的气溶胶卫星资料三维变分同化方法，并通过数值试验验证同化系统的合理性和可靠性。.利用超大城市试验激光雷达组网观测获取的高时间分辨率气溶胶垂直廓线数据，结合地面逐时观测的PM10、PM2.5质量浓度等数据，提出了基于快速辐射传输模式的激光雷达资料三维变分同化方法，并通过数值试验验证同化系统的合理性和可靠性。针对我国华北地区重污染和轻污染过程，开展了云-气溶胶星载激光雷达（CALIPSO）消光系数资料和地面颗粒物同化和预报试验研究，发现气溶胶卫星资料的同化对于地面气溶胶的改进有限，但对于气溶胶垂直分布有明显的改进作。.此外，为了评估我国未来气溶胶激光雷达观测网分布对改善空气质量预报的潜在影响，首次开展了针对中国地区观测布网的观测系统模拟试验（OSSE）研究。结果表明：在模式中同化气溶胶三维廓线信息后，能够更精确地模拟气溶胶的三维结构。激光雷达数据的同化对气溶胶预报改进效果随着激光雷达数量的增加而增加。然而，到达一定数量后，同化对预报改进作用逐渐减少。通过本项目的研究，在国内外权威期刊上发表论文9篇，包括SCI期刊8篇。