非线性平衡方案在三维变分同化系统中的应用  

APPLICATION OF NONLINEAR BALANCE SCHEME IN THREE-DIMENSIONAL VARIATIONAL DATA ASSIMILATION

作　　者：庄照荣[1] 薛纪善[1] 朱宗申 李兴良[1] 

机构地区：[1]中国气象科学研究院 [2]国家气象中心,北京100081

出　　处：《气象学报》2006年第2期137-148,共12页Acta Meteorologica Sinica

基　　金：国家自然科学基金"四维变分同化中物理过程的研究"(40175028);国家"十五"科技攻关计划项目(2004BA607B)

摘　　要：文中考虑气流出现明显的弯曲和辐合时,资料变分同化方案中的风压场间动力学约束问题。在强涡旋、锋面等剧烈变化的系统中,地转平衡和线性平衡方程均不能很好地描述风压场关系,非线性平衡方程考虑了流场曲率的作用,能更恰当地反映风压场的关系。把非线性平衡方案应用于三维变分同化分析系统中,可以得到和天气形势相关联的模式变量背景误差协方差,对热带气旋进行同化试验后得到的分析场更协调。结果表明,非线性平衡方程的应用,可以提高强涡旋系统中三维变分同化分析场的质量,对热带气旋强度预报有一定的改善。In the multivariate analysis, for the practical solution, unbalance parts with the constraint between the variables the variables are divided as the balance parts and the The unbalance parts are designed as analysis variables. So the balance operator is very important to analysis and it will be represented in background error covariance. In simple analysis, the relationship of the wind and the geopotential height field can be described by geostrophic or linear balance equation. The wind and geopotential height field can obey geostrophic balance properly to synoptic scale in middle and high latitude and the difference of geostrophic wind and gradient wind is no more than 10% - 15 %. However, the impact of nonlinear term in balance equation must be considered, for the geostrophic and linear balance can not properly descript the relationship between wind and geopotential height in tropic cyclone system in low latitude where Coriolis parameter is smaller, shear wind is bigger and the curvature is bigger. The impact of nonlinear term in balance equation must be considered in other rapidly changing structures such as frontal structures. The impact of stream divergence and convergence in the relationship of balance between wind and geopotential height field is considered, the every term＇s contribution in balance equation is compared, nonlinear balance constraint in 3D-Var is applied and checking on nonlinear balance scheme and its adjoint scheme are processed. For comparing the linear and nonlinear balance scheme in 3D-Var, single observation test and the analysis in two tropic cyclone systems are processed. The conclusion as follows： （1） The large scale atmospheric flow obeys quasi-geostrophic balance in middle-high latitude, but the β term and the nonlinear term should be considered in low latitude and vortex system. The nonlinear term in balance equation is the biggest and more important when the vortex system is more intensive and the difference of geopotential height gotten from the wind by nonlinear a

关 键 词：变分同化 非线性平衡方程 背景误差协方差 

分 类 号：P458.121.1[天文地球—大气科学及气象学] O241[理学—计算数学]