Improved variational analyses using a nonlinear humidity control variable
Improved variational analyses using a nonlinear humidity control variable
复制标题
使用非线性湿度控制变量改进变分分析
DOI：
10.1002/qj.2073
复制
发表时间：
2013
影响因子：
8.9
通讯作者：
D. Jackson
中科院分区：
文献类型：
--
作者：
N. Ingleby;A. Lorenc;King Ngi Ngan;F. Rawlins;D. Jackson
一种新的湿度分析变量已成功地引入气象局的变分数据同化系统。新变量使用了由非线性归一化和与温度增量的联系组成的变换，该温度增量是背景(预报)湿度的函数。归一化(这是更重要的方面)使新变量的误差更对称，从而更好地由变分成本函数表示。与以前的操作系统一样，在分析步骤中，水蒸气和云被合并为单一的总水变量。这一转变现已在全球系统和有限区域系统中运行。预报的改进--质量和湿度场--在南半球是最大的，对湿度敏感的卫星频道的背景和分析都更适合。结果表明，这种转换特别有利于卫星数据的使用。这种转换减少了分析中的负湿度问题，这些问题在海洋上更为普遍。
A new humidity analysis variable has been successfully introduced into the Met Office's variational data assimilation system. The new variable uses a transformation consisting of a nonlinear normalization and a link with temperature increments that is a function of background (forecast) humidity. The normalization (which is the more important aspect) makes the new variable's errors more symmetrical and thus better represented by the variational cost function. As in the previous operational system, water vapour and cloud are combined into a single total water variable for the analysis step. The transform is now operational in both global and limited‐area systems. The forecast improvements—to the mass as well as the humidity fields—are largest in the Southern Hemisphere and there is a better fit of both background and analysis to humidity‐sensitive satellite channels. The results suggest that the transformation is particularly beneficial for the use of satellite data. The transform reduces the problem of negative humidities in the analysis which were more prevalent over the ocean.