背景误差水平相关结构对四维变分资料同化的影响研究

An impact study of background error horizontal correlation structure on 4DVar

中文关键词:  GRAPES四维变分同化  背景误差水平相关  谱空间方差融合  数值试验

英文关键词:GRAPES 4DVar  Background error horizontal correlation  Variance spectra blending  Numerical experiment

中文摘要:

      为考察GRAPES全球四维变分同化（4DVar）的分析增量在谱空间的时间演变特征，分析当同化时间窗起始时刻与终止时刻背景误差水平相关特征明显不一致时对分析与预报造成的影响，对GRAPES全球4DVar的背景误差水平相关采用二阶自回归模型（SOAR）、集合资料同化生成扰动样本估计的水平相关模型以及基于这两者的背景误差谱空间融合模型进行比较。结果表明，SOAR的分析增量在20波以上的天气尺度波动的分析信息明显不足，而将集合资料同化样本所计算的水平相关的功率谱方差与SOAR功率谱方差进行融合，水平相关特征呈现出多尺度水平相关的特点，可以更好地吸纳观测信息，显著改善北半球形势场、温度与风场预报效果，南半球也有改善，对赤道地区的影响中性。表明研究发展的融合水平相关方案合理、实用。

英文摘要:

      Temporal evolution characteristics of the GRAPES global 4DVar analysis increment in the spectral space is investigated, and the impact on the analysis and forecast is also analyzed when the background error horizontal correlation characteristics at the beginning and end of the data assimilation time window are obviously different. Three types of horizontal correlation model, i.e., the second-order autoregressive model (SOAR), the statistical model from the samples generated by ensemble of data assimilation (EDA), and the blending results of SOAR and EDA, are compared. The results show that the information of synoptic scale in the analysis increment is obviously underestimated by the SOAR model. For the horizontal correlation power spectrum calculated by blending of the SOAR and the EDA, the results show a multi-scale horizontal correlation characteristics, which can better absorb observation information and significantly improve the forecast of geopotential height and temperature in the northern hemisphere. The wind forecast is also improved in the southern hemisphere, while a neutral impact is found in the tropical region. The above results indicate that the merging horizontal correlation scheme developed in this paper is reasonable and practical.