PM_(2.5)和PM_(2.5~10)资料同化及在南京青奥会期间的应用试验

建立了面向PM_(2.5)和PM10观测资料的三维变分同化系统,并在南京地区青奥会期间进行了同化和预报试验.同化系统的控制变量为PM_(2.5)和PM_(2.5~10)(PM10中扣除PM_(2.5)后剩余部分),利用南京地区2014年8月的WRF-Chem模拟结果,估计了PM_(2.5)和PM_(2.5~10)的背景误差协方差,发现在水平和垂直方向上PM_(2.5)的相关系数随距离的衰减均小于PM_(2.5~10),这可能与PM_(2.5)粒径小、生命史长,在大气中传播地更远有关.利用南京及周边区域的134个监测站PM_(2.5)和PM_(10)逐时观测资料,对青奥会期间(2014年8月16~28日)进行滚动同化和预报试验,并利用模式最内层观测资料进行检验分析,结果表明同化对初始场有显著改进,PM_(2.5)和PM10的相关系数均提高53%以上,均方根误差降低55%以上,平均偏差则降低了90%左右;同化试验对其后的预报场也有明显改进,正效应可以持续到20h以后,模式对PM10的预报效果好于PM_(2.5).

Data assimilation and application experiments of PM2.5 and PM2.5~10 during Nanjing Youth Olympic Games

A 3D-VAR assimilation system was established to assimilate the observations of PM_2.5 and PM₁₀, and assimilation and forecast experiments were performed during Nanjing Youth Olympic Games (NYOG). The control variables of this assimilation system were PM_2.5 and PM_2.5~10 (that was the rest of PM₁₀ after taking out PM_2.5). The background error covariances of PM_2.5 and PM_2.5~10 were estimated by using the simulated products of WRF-Chem of August 2014 in Nanjing. The results showed that the decreases of correlation coefficients of PM_2.5 with the distance in the horizontal and vertical directions were less than those of PM_2.5~10, with the possible reason being that the particle size of PM_2.5 was smaller, the life cycle of it was longer and it spread further in the atmosphere. In addition, the WRF-Chem model was run with assimilation during NYOG (from August 16^th to August 28^th, 2014), by using the hourly data of PM_2.5 and PM₁₀ observed from 134 measurement sites around Nanjing. Evaluated with the observations in the innermost of the model area, the experiment results suggested that the aerosol forecasts of the initial fields can be significantly improved by the assimilation. The correlation coefficients of PM_2.5 and PM₁₀ increased by over 53%, the root-mean-square errors of the two reduced by over 55%, and the biases reduced by about 90%. The following aerosol forecasts in positive effect can be obviously improved by the assimilation and the benefit from the assimilation of aerosol can last more than 20hours. The forecast of PM₁₀ was better than that of PM_2.5 by the model.