三维变分同化中多变量平衡约束设计

Design of multivariable balance constraints in three-dimensional variational assimilation

在现代变分同化系统中,背景场误差协方差起着决定观测信息的空间分布特征、匹配不同变量间的关系和保证分析增量平衡的作用。基于NMC(National Meteorology Centre)方法,设计了一个新的多变量平衡约束算子:在物理变换中,构建相对湿度和其余控制变量间的平衡约束算子;同时分别采用经验正交函数方法和递归滤波器来模拟控制变量(ψ,χu,Tu,hru,psu)T的垂直误差协方差和水平误差协方差。利用2009年6月2日到8月9日间WRF模式的预报差值场,对新的背景场误差协方差进行模拟分析。单点观测试验表明,新的背景场误差协方差实现了观测信息在干湿变量之间的传递,而且相对湿度具有与温度相似的增量场分布。

In modem variational data assimilation system, the background error covariance determines the space distribution of observation information and analysis increment balance between control variables. Based on the NMC（ National Meteorology Centre） method,a new multivariable balance constraint operator is designed, and the forecast difference fields of WRF model from 2 June to 9 August 2009 are used to simulate the new background error covariance. In physical transformation, the multivariable balance constraint operator is built among control variables including relative humidity. The empirical orthogonal function method and the recursive filter are used to simulate the vertical and horizontal error covariances of control variables （ψ,Xu,Tu,hru,Psu）^T, respectively. The results of single observation test show that observation information has been passed between the wet and dry variables with new background error covariance, and the increment distribution of relative humidity is similar to the temperature.