Use of potential vorticity for incremental data assimilation
Use of potential vorticity for incremental data assimilation
复制标题
使用位涡进行增量数据同化
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
I. Roulstone
中科院分区：
文献类型：
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作者：
M. Wlasak;Nancy Nichols;I. Roulstone
在数据同化方案中，将质量场和风场分解为平衡流和非平衡流是定义协方差模型过程的一部分。通常假设气流的动态平衡部分仅由风的旋转部分近似，而旋转部分是从水平动量的亥姆霍兹分解中获得的（例如，从平衡方程中诊断性地推导出相关的平衡压力）。不平衡流则由发散和残余不平衡压力表示。动量的旋转部分是总平衡流的良好近似的假设仅在某些情况下有效。我们提出了一种新的方法，结合流态的依赖性，在这里，我们假设的平衡部分的流量近似，而不是由一个线性化的位涡增量。我们在定义在半球上的浅水方程的背景下，这样的配方的好处。版权所有© 2006年皇家气象学会
Decomposing the mass and wind fields in a data assimilation scheme into balanced and unbalanced flow is part of the process of defining a covariance model. It is not uncommon to assume that the dynamic balanced part of the flow is approximated solely by the rotational part of the wind, which is obtained from a Helmholtz decomposition of the horizontal momentum (with an associated balanced pressure being diagnostically inferred from a balance equation, for example). The unbalanced flow is then represented by the divergence and the residual unbalanced pressure. The assumption that the rotational part of the momentum is a good approximation to the total balanced flow is only valid in certain regimes. We propose a new approach that incorporates flow regime dependence, where we assume that the balanced part of the flow is approximated instead by a linearized potential vorticity increment. We show the benefit of such a formulation in the context of shallow‐water equations defined on a hemisphere. Copyright © 2006 Royal Meteorological Society