An investigation of incremental 4D‐Var using non‐tangent linear models
An investigation of incremental 4D‐Var using non‐tangent linear models
复制标题
使用非相切线性模型研究增量 4D-Var
DOI：
10.1256/qj.04.20
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发表时间：
2005
影响因子：
8.9
通讯作者：
N. Nichols
中科院分区：
文献类型：
--
作者：
A. Lawless;S. Gratton;N. Nichols
我们研究了增量四维变分资料同化(4D-Var)在内环内采用切线型模式近似时的收敛问题。利用一维浅水方程的半隐式半拉格朗日模式，分别用精确的切线型模式和非精确型的线性模式(扰动预报模式)进行了资料同化试验。我们发现，这两种同化以相似的速度收敛，分析也是相似的，它们之间的差异取决于观测中的噪声量。为了理解数值结果，我们将增量4D-Var算法表示为求解最小二乘问题的高斯-牛顿迭代，并考虑了它的不动点。版权所有(C)2005皇家气象学会。
We investigate the convergence of incremental four‐dimensional variational data assimilation (4D‐Var) when an approximation to the tangent linear model is used within the inner loop. Using a semi‐implicit semi‐Lagrangian model of the one‐dimensional shallow water equations, we perform data assimilation experiments using an exact tangent linear model and using an inexact linear model (a perturbation forecast model). We find that the two assimilations converge at a similar rate and the analyses are also similar, with the difference between them dependent on the amount of noise in the observations. To understand the numerical results, we present the incremental 4D‐Var algorithm as a Gauss–Newton iteration for solving a least‐squares problem and consider its fixed points. Copyright © 2005 Royal Meteorological Society.