利用云对称性假定分析微波成像仪全天空偏差特征

Analysis of the Observation Errors of FY-3C MWRI Radiance in the All-Sky Assimilation with Symmetric Cloud Assumption

星载微波成像仪全天空观测资料包含了云和降水的信息,但全天空的观测误差不满足资料同化中观测误差为高斯分布的要求。根据欧洲中期天气预报中心提出的云对称性假定,建立了风云三号C星微波成像仪(Fengyun-3C Microwave Radiation Imager,FY-3C MWRI)资料全天空观测误差模型,选取超强台风玛莉亚和利奇马作为研究个例,将全天空观测辐射率进行质量控制和标准化之后分析了全天空的初估场偏离值(first-guess departure,FG departure)特征。结果显示:在云对称性假定下,FY-3C MWRI所有通道的全天空初估场偏离值均接近高斯分布,可以用于观测资料的误差分析;较传统微波晴空资料误差分析模型,基于云对称性假定的全天空观测误差分析模型新增了43.90%~54.63%的卫星观测资料分析,新增观测资料主要来自台风螺旋云带和云墙部分区域。文章初步挖掘了FY-3C MWRI全天空观测资料的可同化潜力,对进一步提高国产风云卫星微波资料在数值预报中的利用率有实际应用价值。

All-sky observations of space-based microwave imager contain information of strong meteorological sensitivity related to cloud and precipitation.But the observation error in all-sky data assimilation is apparently non-Gaussian behavior which cannot meet the basic assumption that the observation error is Gaussian in the data assimilation.In this research,a“symmetric cloud”dependent all-sky observation error model developed by European Centre for Medium-Range Weather Forecasts(ECMWF)was used for Fengyun-3C microwave radiation imager(FY-3C MWRI),observations during super typhoons“Maria”and“Lekima”were selected and the all-sky observation error was analyzed after quality control and normalization.The results show that the all-sky first-guess departures normalized by the symmetric error model become to near Gaussian distribution so that the data can be used in the data assimilation.In addition,all-sky approach brings 43.90%-54.63%more data than clear sky,with the biggest increases in the area of the outer spiral cloud band and cloud wall of typhoon.This result preliminarily demonstrates the assimilation potential of FY-3C MWRI all-sky observation data,and the utilization of observation data from the current Fengyun series microwave imagers is expected to improve the numerical weather prediction.