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首页> 外文期刊>Journal of Physical Oceanography >Eddy Amplitudes in Baroclinic Turbulence Driven by Nonzonal Mean Flow: Shear Dispersion of Potential Vorticity
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Eddy Amplitudes in Baroclinic Turbulence Driven by Nonzonal Mean Flow: Shear Dispersion of Potential Vorticity

机译：非区域平均流驱动斜压湍流的涡流振幅：潜在涡度的剪切分散

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As in the midlatitude atmosphere, midocean eddies are primarily generated by baroclinically unstable mean currents. In contrast to the atmosphere, however, oceanic currents are significantly nonzonal. Even weak nonzonal currents are linearly unstable since β does not suppress growing meridional waves. Theories for the nonlinear equilibration of baroclinic instability, and hence theories for the amplitudes of midocean eddies, must therefore take into account the different dynamics of nonzonal flow. It is shown here that the amplitude of fully developed baroclinic turbulence due to nonzonal shears differs from that due to zonal shears primarily in the nature of the eddy generation. Since β will act to create large-scale zonal jet structures regardless of the generation source, the nature of eddy fluxes of potential vorticity (the source of eddy energy) in the zonal and meridional directions are fundamentally different. The cross-jet mixing has been shown previously to obey a mixing-length scaling, and this corresponds to the generation due to unstable zonal flow. The along-jet mixing, which corresponds to the generation due to the meridional shear, is shown here to be best described by a shear dispersion model. The resulting flux is orders of magnitude higher than in the cross-jet direction, and thus eddy energies driven by baroclinically unstable mean flows with a nonzero meridional component are much larger. This provides an explanation for recently reported results. Moreover, given recent observational and modeling studies showing the ubiquitous presence of zonal jets in the oceans, the results presented here indicate a powerful source of eddy energy.
机译：与中纬度大气一样，中洋涡旋主要是由斜压不稳定的平均流产生的。但是，与大气层相比，洋流明显是非区域性的。由于β不能抑制子午波的生长，因此即使是弱的非区域电流也线性不稳定。因此，斜压不稳定的非线性平衡理论以及中洋涡旋振幅的理论都必须考虑非区域流动的不同动力学。此处显示出，主要由于涡旋产生的性质，由非区域性剪切引起的完全斜压湍流的振幅不同于由于区域性剪切引起的斜压湍流的幅度。由于β会产生大型的纬向射流结构，而不管其产生源如何，因此在纬向和子午方向上潜在涡度的涡流性质（涡能量的来源）是根本不同的。交叉射流混合先前已显示出遵循混合长度比例，并且这对应于由于不稳定的纬向流动而产生的情况。沿射流混合，对应于由于子午剪切产生的，这里用剪切扩散模型可以最好地描述。产生的通量比横向喷射方向高几个数量级，因此，由斜向不稳定的平均流（具有非零子午分量）驱动的涡流能量要大得多。这为最近报告的结果提供了解释。此外，鉴于最近的观测和建模研究表明海洋中普遍存在纬向射流，此处给出的结果表明了涡流能量的强大来源。

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