The Modification of Long Planetary Waves by Homogeneous Potential Vorticity Layers
The Modification of Long Planetary Waves by Homogeneous Potential Vorticity Layers
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DOI：
10.1175/1520-0485(1999)029
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发表时间：
1999-03
影响因子：
3.5
通讯作者：
R. D. Szoeke;D. Chelton
中科院分区：
文献类型：
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作者：
R. D. Szoeke;D. Chelton
研究了海洋中长行星波的传播速度明显快于经典长斜压罗斯贝波的机制。该机制取决于中间密度层向极地增厚以及近地表层和深层的伴随减薄。质量分布的这些特征与众所周知的中间密度层中位涡的均质化以及表面附近和深度处显着升高的经向位涡梯度相关。该机制在一个简单的三层模型中进行了探索，其中中间层具有零位涡梯度，并且夹在具有大位涡梯度的表面层和具有适度位涡梯度的底层之间。行星波的有效相速度仅仅是在各个层界面上传播的虚拟斜斜罗斯贝波的相速度之和，就好像其他界面不存在并且好像没有平均垂直剪切一样。该机制还针对连续模型进行了检查，该模型在整个内部具有零位涡梯度，而在表面和底部附近具有较大的虚拟位涡梯度。这些模型中的行星波向西传播的速度是斜压罗斯贝波穿过具有相同垂直分层但没有平均垂直切变的海洋时的两倍。对罗斯贝波加速的这种解释补充了最近基于存档水文数据的地转速度剖面的行星波相速度的详细理论计算。
A mechanism by which long planetary waves in the ocean may propagate significantly faster than the classical long baroclinic Rossby waves is investigated. The mechanism depends on the poleward thickening of intermediate density layers and the concomitant thinning of near-surface and deep layers. These features of the mass distribution are associated with the well-known homogenization of potential vorticity in intermediate density layers and with significantly elevated meridional potential vorticity gradients near the surface and somewhat at depth. The mechanism is explored in a simple three-layer model, in which the middle layer has zero potential vorticity gradient and is sandwiched between a surface layer with large potential vorticity gradient and a bottom layer with modest potential vorticity gradient. The effective phase speed of the planetary waves is merely the sum of the phase speeds of virtual baroclinic Rossby waves propagating on the individual layer interfaces as though the other interface were not there and as though there were no mean vertical shear. The mechanism is also examined for a continuous model with zero potential vorticity gradient throughout the interior and large virtual potential vorticity gradients near the surface and bottom. Planetary waves in these models can propagate westward up to twice as fast as baroclinic Rossby waves would through an ocean with the same vertical stratification, but no mean vertical shear. This explanation of the Rossby wave speedup complements a recent detailed theoretical calculation of planetary-wave phase speeds based on geostrophic velocity profiles from archived hydrographic data.