Development of NAVDAS-AR: non-linear formulation and outer loop tests
Development of NAVDAS-AR: non-linear formulation and outer loop tests
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DOI：
10.1111/j.1600-0870.2006.00148.x
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发表时间：
2006-01
期刊：
影响因子：
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通讯作者：
T. Rosmond;Liang Xu
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文献类型：
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作者：
T. Rosmond;Liang Xu
NAVDAS-AR是美国海军3DVAR数据同化系统NAVDAS（海军研究实验室大气变分数据同化系统）的4DVAR扩展，其中AR代表加速表示器。与NAVDAS一样，NAVDAS-AR是在观测空间中投射的，并且是4DVAR算法的观测空间公式，与欧洲中期天气预报中心4DVAR系统相反，该系统是分析空间算法。在本文中，我们将展示如何内环线性解决方案可以增加外循环迭代过程，引入非线性效应的形式，一阶泰勒级数展开。然后将非线性问题迭代地求解为线性问题序列。我们展示了外环策略的结果，其中第一环，“线性”解决方案，在第二外环中通过在观测创新的计算中的泰勒级数项和关于从第一环的解决方案的分析“轨迹”线性化的背景模型的线性化形式来修改。我们还展示了外环策略如何更好地同化地面风速和可降水量的观测结果，与操作NAVDAS相比。
NAVDAS-AR is the 4DVAR extension of the United States Navy’s operational 3DVAR data assimilation system, NAVDAS (Naval Research Laboratory Atmospheric Variational Data Assimilation System), where AR stands for accelerated representer. Like NAVDAS, NAVDAS-AR is cast in observation space, and is an observation space formulation of the 4DVAR algorithm, in contrast to the European Centre for Medium-Range Weather Forecasts 4DVAR system, which is an analysis space algorithm. In this paper we show how an inner loop linear solution can be augmented by an outer loop iteration procedure that introduces non-linear effects in the form of a first-order Taylor series expansion. The non-linear problem is then solved iteratively as a sequence of linear problems. We show results of the outer loop strategy, where the first loop, the ‘linear’ solution, is modified in the second outer loop by both a Taylor series term in the calculation of the observation innovations, and a linearized form of the background model that is linearized about an analysis ‘trajectory’ from the solution of the first loop. We also show results of how the outer loop strategy allows better assimilation of observations of surface wind speed and precipitable water, compared to the operational NAVDAS.