Ensemble estimation of background‐error variances in a three‐dimensional variational data assimilation system for the global ocean
Ensemble estimation of background‐error variances in a three‐dimensional variational data assimilation system for the global ocean
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DOI：
10.1002/qj.412
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发表时间：
2009-04
影响因子：
8.9
通讯作者：
N. Daget;A. Weaver;M. Balmaseda
中科院分区：
文献类型：
--
作者：
N. Daget;A. Weaver;M. Balmaseda
本文研究了三维变分数据同化（3D - Var）系统中温度和盐度的背景误差标准差（σb）对两种与洋流相关的公式的敏感性。第一个公式是根据背景温度场和盐度场的垂直梯度对σb进行经验参数化，而第二个公式则采用了更复杂的方法，从背景状态集合的扩散中推导出σb。通过明确扰动用于强迫模型的地表通量（风应力、淡水和热）和同化过程中使用的观测值（温度和盐度剖面），形成了这些综合。在1993 - 2000年期间的两次3D - Var循环试验中对这两种公式进行了比较。在这两个实验中，观测误差标准偏差（σo）是地理依赖的，并从同化前的模型数据比较中估计。另一个采用参数化σb但更简单的σo公式的3D - Var实验和一个不涉及数据同化的对照实验也进行了比较。
This paper studies the sensitivity of global ocean analyses to two flow‐dependent formulations of the background‐error standard deviations (σb) for temperature and salinity in a three‐dimensional variational data assimilation (3D‐Var) system. The first formulation is based on an empirical parameterization of σb in terms of the vertical gradients of the background temperature and salinity fields, while the second formulation involves a more sophisticated approach that derives σb from the spread of an ensemble of background states. The ensembles are created by explicitly perturbing both the surface fluxes (wind stress, fresh water and heat) used to force the model and the observations (temperature and salinity profiles) used in the assimilation process. The two formulations are compared in two cycled 3D‐Var experiments for the period 1993‐‐2000. In both experiments, the observation‐error standard deviations (σo) are geographically dependent and estimated from a model‐data comparison prior to assimilation. An additional 3D‐Var experiment that employs the parametrized σb but a simpler σo formulation, and a control experiment involving no data assimilation, were also conducted and used for comparison.