基于Hybrid EnSRF-En3DVar的雷达资料同化研究
投稿时间: 2015-03-04  最后修改时间: 2015-03-04  点此下载全文
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闵锦忠 南京信息工程大学 minjz@nuist.edu.cn. 
中文摘要:利用WRF模式,构建Hybrid EnSRF-En3DVar同化系统,该系统使用EnSRF方案直接更新集合扰动。集合协方差权重敏感性试验发现:当集合协方差权重分别为0.25,0.5,0.75时,同化效果优于3DVar试验;当背景误差协方差全为集合协方差时,分析场最差;分析场的最优估计由集合协方差权重0.75试验给出。雷达不同要素同化敏感性试验表明,联合同化雷达径向风及反射率能有效改善大气湿度场和风场,但对风场的改善效果不如仅同化雷达径向风试验。将EnSRF更新集合扰动方案与扰动观测更新集合扰动方案综合分析发现,扰动观测方案集合离散度较小,执行耗时;EnSRF更新集合扰动方案优于扰动观测方案。
中文关键词:资料同化  Hybrid EnSRF-En3DVar  多普勒雷达  台风
 
Study of assimilating Doppler radar data with hybrid EnSRF-En3DVar method
Abstract:A hybrid ensemble square root filter and three-dimensional ensemble- variational (EnSRF-En3DVar) data assimilation (DA) system is developed. The En3DVar hybrid system is built on Weather Research and Forecasting Model (WRF) three-dimensional variational data assimilation (3DVar) framework. It is coupled with an EnSRF system, which provides ensemble perturbations. The system is applied to the assimilation of simulated data from two radars for typhoon Saomai. Some experiments are performed to answer questions about how flow-dependent covariance estimated from the forecast ensemble can be best used in the hybrid EnSRF-En3DVar system. It is found that experiments with 30 ensemble members and a relative weighting (0.25,0.5,0.75) for the ensemble covariance lead to better analyses from the En3DVar hybrid system than the corresponding 3DVar. When using pure ensemble covariance, En3DVar hybrid system performs the worst while a relative weighting (0.75) for the ensemble covariance gets the best analysis. The further analysis of the joint assimilation of radial velocity and reflectivity shows that: joint assimilation can improve the initial analysis of humidity information but did not produce noticeable improvement in wind field over the separate assimilation of radial velocity. In addition, the method to generate the ensemble perturbations also be compared, the “perturbed observation” method suffers small ensemble spread and time-consuming cost, so the EnSRF method is superior to perturbed observation method to generate the ensemble perturbations.
keywords:Data assimilation  Hybrid EnSRF-En3DVar  Doppler radar  Typhoon
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