Use of cloud‐cleared radiances in three/four‐dimensional variational data assimilation
Use of cloud‐cleared radiances in three/four‐dimensional variational data assimilation
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DOI：
10.1002/qj.49712051707
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发表时间：
1994-04
影响因子：
8.9
通讯作者：
E. Andersson;J. Pailleux;J. Thepaut;J. Eyre;A. Mcnally;G. Kelly;P. Courtier
中科院分区：
文献类型：
--
作者：
E. Andersson;J. Pailleux;J. Thepaut;J. Eyre;A. Mcnally;G. Kelly;P. Courtier
描述了在三维/四维变分数据同化方案中直接使用TOVS （TIROS操作垂直测深仪）云清除辐射。该方案采用了快速辐射传输模型及其伴随模型。辐射量与所有其他观测数据一起使用。在一定的质量/风平衡约束条件下，同时分析了质量、风和湿度的全球谱场，这些约束条件控制了重力波进入分析的程度。这样就避免了后续初始化的需要。因此，该方案将检索、分析和初始化在一个步骤中结合起来，使辐射、常规数据和背景（六小时预报）中所含信息的更优组合成为可能。在光谱截断T63处，将TOVS辐射和常规数据的全局三维变分分析（3D-Var）与ECMWF操作最优插值方案进行比较，该方案使用温度和湿度剖面形式的TOVS辐射信息，使用一维变分方法检索。3D-Var的结果与相同分辨率下的操作分析结果吻合较好。在四维方案（4D-Var）的应用中，同时使用了24小时的数据。在4D-Var中，通过预测模型及其伴随物的演化来保证时间一致性。利用ECMWF绝热预报模式（光谱分辨率T42），我们发现4D-Var能够从模式的动力学中提取额外的信息。我们特别展示了使用对湿度敏感的TOVS通道对热带风场的影响。
The direct use of TOVS (TIROS Operational Vertical Sounder) cloud-cleared radiances in a three/four-dimensional variational data assimilation scheme is described. This scheme uses a fast radiative transfer model and its adjoint. Radiances are used together with all the other observational data. Global spectral fields of mass, wind and humidity are analysed simultaneously under certain mass/wind balance constraints which control the degree to which gravity waves enter into the analysis. In this way the need for a subsequent initialization is avoided. The scheme thus combines retrieval, analysis and initialization in one step and makes it possible to achieve a more optimal combination of the information contained in the radiances, the conventional data and the background (a six-hour forecast). At spectral truncation T63, a global three-dimensional variational analysis (3D-Var) of TOVS radiances and conventional data is compared with the ECMWF operational Optimum Interpolation scheme, which uses TOVS radiance information in the form of profiles of temperature and humidity, retrieved using a one-dimensional variational method. The results of 3D-Var are in good agreement with the operational analysis at the same resolution. In an application of the four-dimensional scheme (4D-Var), data covering a period of 24 hours were used simultaneously. In 4D-Var consistency in time is ensured through the evolution of the forecast model and its adjoint. Using the adiabatic version of the ECMWF forecast model (spectral resolution T42) we show that 4D-Var is able to extract additional information from the dynamics of the model. In particular we show an impact on the tropical wind field from the use of the humidity-sensitive TOVS channels.