王铁,穆穆. 2008. REM模式伴随系统的建立及其四维变分资料同化初步试验[J]. 气象学报, 66(6):955-967, doi:10.11676/qxxb2008.086
REM模式伴随系统的建立及其四维变分资料同化初步试验
A REM adjoint system and its data assimilation experiments of 4D-Var
投稿时间:2007-06-26  
DOI:10.11676/qxxb2008.086
中文关键词:  REM模式,伴随系统,四维变分资料同化
英文关键词:REM model, Adjoint system, 4D-Var data assimilation
基金项目:国家自然科学基金项目(40233029、40221503),中国科学院知识创新工程方向项目(KZCX2-208),大气科学和地球流体力学数值模拟国家重点实验室开放课题
作者单位
王铁 1. 中国科学院大气物理研究所LASG北京100029 2. 解放军理工大学气象学院南京211101 
穆穆 中国科学院大气物理研究所LASG北京100029 
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中文摘要:
      Regional-Eta-Coordinate-Model(REM)中尺度模式对中国区域性降水显示出公认的较高预报能力,建立其四维变分资料同化系统是完善该模式,进一步提高其预报效果的重要工作。本研究编写了REM模式的切线性模式和伴随模式,介绍了建立REM模式伴随系统的过程,并利用实际天气个例资料,分别对REM模式的切线性模式、伴随模式及定义的目标函数梯度进行了正确性检验,检验结果表明对REM模式的切线性模式及伴随模式编写是成功的。利用REM模式的伴随系统,对1998年06月08日00时到09日00时和2000年08月01日00时到02日00时两个实际天气个例进行了四维变分资料同化试验。从数值试验的结果分析可以看到,进行四维变分资料同化后,两个天气个例在预报结束时刻其预报结果对风场和湿度场的预报都有明显改善,对温度场和高度场的预报也有所改善。对于累积降水的预报,两个个例利用四维变分资料同化后得到的初始场进行的预报结果则有较大不同,在个例1中,变分同化后对降水中心的位置和降水强度的预报都有明显改善,预报结果更接近于观测场;个例2中,变分同化后对降水中心位置和强度的预报则没有改善,产生这种现象的原因可能是由于定义的目标函数中没有加进背景场项,也可能是由于采用的观测资料时次比较少,还需要进一步进行研究和试验。
英文摘要:
      The Regional Eta Coordinate Model(REM)has shown an acceptable good forecast ability to the regional heavy rainfall of China in recent years, and developing a Four Dimension Data assimilation system(4D-Var) for the REM is an important step to consummate the model as well as to improve its forecast ability. The tangent linear model and adjoint model codes were written according to the “code to code” rule, and the establishment process of the REM adjoint modeling system is introduced in details. The verification of the tangent linear model and adjoint model of the REM model was performed using a lot of observational data, and the correctness of the gradient of the given cost function was also checked. In the verifications of the tangent linear model and cost function, when the magnitude of perturbations reduced, the verification results approached to 1.0, and when the rounding error of computer increased, the verification results departed off 1.0, thus showing that the coding of the tangent linear model is successful and the gradient of cost function is correct calculated. In the verification of the adjoint model, the values at left and right hand side of algebraic formula are the same with 13 digit accuracy. The above results indicate that the REM adjoint modeling system is successfully established. Applying the REM adjoint modeling system, two 4D-Var experiments and extended forecast were performed using the Observational data of two weather cases (00:00 UTC 8 June 1998 to 12:00 UTC 8 June 1998 and 00:00 UTC 1 August 20:00 to 12:00 UTC 1 August 2000). The results show that forecasts of temperature, wind speed and specify humidity using the 4D-Var -assimilated initial data are all improved at both the end of the assimilation window and the end of the forecast time. But forecast results of rainfall are different in the two cases: the location and amount of the accumulated rainfall are closer to the observation in the first case, while in the second case there is no significant improvement. The reason for results in the second case maybe two aspects: the first is that the definition of the cost function is too simple during the primary numerical experiments of 4D-Var, the background term was not considered in the cost function, the errors caused by the numerical model during the 4D-Var were not controlled. And further more the accumulated rainfall was not considered in the cost function too, which affected the 4D-Var assimilated initial data, and especially in the convective weather process, the effect was more obviously; the second aspect is that the observational data used during the 4D-Var was fewer in the assimilation widows, just one at the end of the assimilation windows. This case will be studied in the further research.
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