Transformed Eulerian-Mean Theory. Part I: Nonquasigeostrophic Theory for Eddies on a Zonal-Mean Flow
Transformed Eulerian-Mean Theory. Part I: Nonquasigeostrophic Theory for Eddies on a Zonal-Mean Flow
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变换欧拉平均理论。
DOI：
10.1175/jpo-2669.1
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发表时间：
2005
影响因子：
3.5
通讯作者：
R. Ferrari
中科院分区：
文献类型：
--
作者：
R.;Alan Plumb;R. Ferrari
讨论了在 z 坐标中使用变换欧拉平均 (TEM) 方法的纬向平均流中非地转涡流输运的理论形式。通过使用安德鲁斯和麦金泰尔对“准斯托克斯流函数”的坐标独立定义，有人认为，与采用广泛使用的准地转定义相比，可以更容易地处理表面边界条件。与“残余平均环流”一起，“残余涡流”的概念自然地出现在 TEM 框架内，并且有人认为，正是这种残余涡流，而不是“原始”涡流，可以合理地预期是下降的。这种区别对于 Ertel 位涡 (PV) 尤为重要。作者展示了如何生成一组封闭的变换平均方程，以及涡流强迫如何出现在 TEM 动量方程中。在绝热条件下，“涡流阻力”与PV沿平均等密度线的残余涡通量成正比；在接近地表的非绝热层中，它更复杂，但对于小罗斯贝数（不假设小等重斜率）变得非常简单。
A theoretical formalism for nongeostrophic eddy transport in zonal-mean flows, using a transformed Eulerian-mean (TEM) approach in z coordinates, is discussed. By using Andrews and McIntyre’s coordinate-independent definition of the “quasi-Stokes streamfunction,” it is argued that the surface boundary condition can be dealt with more readily than when the widely used quasigeostrophic definition is adopted. Along with the “residual mean circulation,” the concept of “residual eddy flux” arises naturally within the TEM framework, and it is argued that it is this residual eddy flux, and not the “raw” eddy flux, that might reasonably be expected to be downgradient. This distinction is shown to be especially important for Ertel potential vorticity (PV). The authors show how a closed set of transformed mean equations can be generated, and how the eddy forcing appears in the TEM momentum equations. Under adiabatic conditions, the “eddy drag” is just proportional to the residual eddy flux of PV along the mean isopycnals; in the diabatic layer close to the surface, it is more complicated, but becomes very simple for small Rossby number (without any assumption of small isopycnal slope).