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首页> 外文期刊>Journal of Physical Oceanography >The Instability of Rossby Basin Modes and the Oceanic Eddy Field
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The Instability of Rossby Basin Modes and the Oceanic Eddy Field

机译：Rossby盆地模式的不稳定性和海洋涡流场

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Low-frequency, large-scale baroclinic Rossby basin modes, resistant to scale-dependent dissipation, have been recently theoretically analyzed and discussed as possible efficient coupling agents with the atmosphere for interactions on decadal time scales. Such modes are also consistent with evidence of the westward phase propagation in satellite altimetry data. In both the theory and the observations, the scale of the waves is large in comparison with the Rossby radius of deformation and the orientation of fluid motion in the waves is predominantly meridional. These two facts suggest that the waves are vulnerable to baroclinic instability on the scale of the deformation radius. The key dynamical parameter is the ratio Z of the transit time of the long Rossby wave to the e-folding time of the instability. When this parameter is small the wave easily crosses the basin largely undisturbed by the instability; if Z is large the wave succumbs to the instability and is largely destroyed before making a complete transit of the basin. For small Z, the instability is shown to be a triad instability; for large Z the instability is fundamentally similar to the Eady instability mechanism. For all Z, the growth rate is on the order of the vertical shear of the basic wave divided by the deformation radius. If the parametric dependence of Z on latitude is examined, the condition of unit Z separates latitudes south of which the Rossby wave may successfully cross the basin while north of which the wave will break down into small-scale eddies with a barotropic component. The boundary between the two corresponds to the domain boundary found in satellite measurements. Furthermore, the resulting barotropic wave field is shown to propagate at speeds about 2 times as large as the baroclinic speed, and this is offered as a consistent explanation of the observed discrepancy between the satellite observations of Chelton and Schlax and simple linear wave theory. Here it is suggested that Rossby basin modes, if they exist, would be limited to tropical domains and that a considerable part of the observed midlatitude eddy field north of that boundary is due to the instability of wind-forced, long Rossby waves.
机译：低频，大规模斜斜的罗斯比盆地模式，对比例依赖的耗散具有抵抗力，最近已经在理论上进行了分析和讨论，作为与大气相互作用的可能有效耦合剂，以年代际时间尺度为基础。这种模式也与卫星测高数据向西传播的证据一致。在理论和观测中，与Rossby变形半径相比，波浪的规模都很大，并且波浪中流体运动的方向主要是子午线。这两个事实表明，在变形半径范围内，波浪容易受到斜压不稳定的影响。关键的动力学参数是长Rossby波的传播时间与不稳定性的电子折叠时间之比Z。当此参数小时，波浪很容易在很大程度上不受不稳定因素影响而越过盆地。如果Z很大，则波浪会屈服于不稳定性，并在完全流过盆地之前被破坏很大。对于小Z，不稳定性显示为三重轴不稳定性；对于大Z，不稳定性从根本上类似于Eady不稳定机制。对于所有Z，增长率约为基波的垂直剪切除以变形半径。如果检查Z对纬度的参数依赖性，则Z单元的条件会将纬度以南分离，其中Rossby波可以成功地穿过盆地，而纬度以北将分解为具有正压分量的小涡旋。两者之间的边界对应于卫星测量中发现的域边界。此外，所显示的正压波波场以大约两倍于斜压波速度的速度传播，这可以作为对Chelton和Schlax卫星观测与简单线性波理论之间观测到的差异的一致解释。在这里建议罗斯比盆地模式（如果存在的话）将限于热带地区，并且在该边界以北观察到的中纬度涡流场的相当一部分是由于长的罗斯比长波的风力不稳定性所致。

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