WRF模式三维变分中背景误差协方差估计  

Estimating Background Error Covariance in Regional 3DVAR of WRF

作　　者：王曼[1,2] 李华宏[3] 段旭[1] 刘建宇[1] 符睿[1] 陈新梅[1] 

机构地区：[1]云南省气象科学研究所,昆明650034 [2]中国气象局成都高原气象研究所,成都610071 [3]云南省气象台,昆明650034

出　　处：《应用气象学报》2011年第4期482-492,共11页Journal of Applied Meteorological Science

基　　金：中国气象局成都高原气象研究所开放基金(LPM2009012);云南省科技攻关及高新技术计划(2006SG25);云南省面上基金项目(2009CD145)

摘　　要：利用WRF模式2008年5—10月逐日预报结果,通过NMC方法进行背景误差协方差(B)估计。给出其结构特征,进行单点数值试验,并利用不同B进行1个月的数值模拟试验,检验模拟降水效果。结果表明:通过单点数值试验验证估算的B结构合理。不同的B,资料同化过程差别较大,应用重新统计的B,同化效率更高,目标函数收敛更稳定。模式模拟降水预报效果有所差别,经过重新统计与预报模式区域和各种参数相匹配的B,模式预报效果在中雨及以上量级优于通用的B预报效果。因此,在应用三维变分同化系统时,重新统计B非常必要。In order to explore the statistical structure of background error covariance （B） and its impact on initial field and three-dimensional variational data assimilation system, based on day by day WRF model forecast data from May to October in 2008, B is estimated using NMC method. The statistical structure of B is analyzed and validated with single ideal experiment, showing that it can reasonably reflect the geostrophie balance relationships and the relationships among multivariable in middle and lower latitudes. The characteristics of B structure are presented as well. A B file provided in three-dimensional variational data assimilation system, it is a generic background error statistics file called CV3-B that can be used for any resolution or area case. The CV3-B is the NCEP background error covariance, which is estimated in grid space by the NMC method. The statistics are esti mated with the differences of 24 and 48 hour GFS forecasts with T170 resolution valid at the same time for 357 cases distributed over a period of one year. The major differences between these two kinds of B are the vertical covariance. CV3-B uses the vertical recursive filter to model the vertical covariance but the modified B uses the empirical orthogonal function （EOF） to represent the vertical covariance. In order to compare the difference of the two B in detail, a simulation experiment for June 2009 with two different B are performed to comparatively analyze the initial fields and precipitation distributing of strong rainfall case,and test the simulation effect in a month precipitation. The results show that different B lead to great differences in data assimilation processes. With the same background fields and observation, the minimizing convergence standards are equal to 0.01, the iterative step is about twenty using updated B, while the iterative step is about forty using CV3-B. And using updated B, for most instances it＇s monotonic decrea- sing during the iteration except for few iterative steps, and the decrease velocity

关 键 词：背景误差协方差 单点试验 数值试验 WRF模式 

分 类 号：P456.7[天文地球—大气科学及气象学]