A Regime-dependent balanced control variable based on potential vorticity
A Regime-dependent balanced control variable based on potential vorticity
复制标题
基于位涡的制度相关平衡控制变量
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
M. Cullen
中科院分区：
文献类型：
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作者：
R. Bannister;M. Cullen
本文论证了旋转风不是变分同化的主导控制变量的最佳选择，并提出了一种替代方案并进行了检验。在大多数全球变分同化系统中，旋转风参数被用作近似表示同化增量的平衡分量的实用方法。实际上，旋风被视为潜在涡度的代表，但在以小Burger数为特征的流动状态中，旋风可能不是一个好的选择。本文报道了基于位涡的另一组控制变量。这导致了气象局变分同化系统的背景误差协方差的新公式，这导致了流量依赖性。它使用与传统方案类似的平衡关系，但承认存在不平衡的旋转风，这是与新的反平衡关系一起使用的。对新方案进行了描述，并使用诊断样本对其性能进行了评估，并与传统方案进行了比较。
In this paper it is argued that rotational wind is not the best choice of leading control variable for variational data assimilation, and an alternative is suggested and tested. A rotational wind parameter is used in most global variational assimilation systems as a pragmatic way of approximately representing the balanced component of the assimilation increments. In effect, rotational wind is treated as a proxy for potential vorticity, but one that it is potentially not a good choice in flow regimes characterised by small Burger number. This paper reports on an alternative set of control variables which are based around potential vorticity. This gives rise to a new formulation of the background error covariances for the Met Office’s variational assimilation system, which leads to flow dependency. It uses similar balance relationships to traditional schemes, but recognises the existence of unbalanced rotational wind which is used with a new anti-balance relationship. The new scheme is described and its performance is evaluated and compared to a traditional scheme using a sample of diagnostics.