Mesoscale eddies are ubiquitous dynamical features that tend to propagate westward and disappear along ocean western boundaries. Using a multiscale observational study, we assess the extent to which eddies dissipate via a direct cascade of energy at a western boundary. We analyze data from a ship‐based microstructure and velocity survey, and an 18‐month mooring deployment, to document the dissipation of energy in anticyclonic and cyclonic eddies impinging on the topographic slope east of the Bahamas, in the North Atlantic Ocean. These observations reveal high levels of turbulence where the steep and rough topographic slope modified the intensified northward flow associated with, in particular, anticyclonic eddies. Elevated dissipation was observed both near‐bottom and at mid depths (200–800 m). Near‐bottom turbulence occurred in the lee of a protruding escarpment, where elevated Froude numbers suggest hydraulic control. Energy was also radiated in the form of upward‐propagating internal waves. Elevated dissipation at mid depths occurred in regions of strong vertical shear, where the topographic slope modified the vertical structure of the northward eddy flow. Here, low Richardson numbers and a local change in the isopycnal gradient of potential vorticity (PV) suggest that the elevated dissipation was associated with horizontal shear instability. Elevated mid‐depth dissipation was also induced by topographic steering of the flow. This led to large anticyclonic vorticity and negative PV adjacent to the topographic slope, suggesting that centrifugal instability underpinned the local enhancement in dissipation. Our results provide a mechanistic benchmark for the realistic representation of eddy dissipation in ocean models.

中文翻译：

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在西方边界的“亚尺度”亚尺度尺度过程的“中尺度”涡流消散

中尺度涡是普遍存在的动力学特征，往往向西传播并沿海洋西部边界消失。使用多尺度观察性研究，我们评估了涡流在西边界通过能量的直接级联消散的程度。我们分析了基于船的微观结构和速度调查以及18个月的系泊部署中的数据，以记录撞击北大西洋巴哈马以东地形坡度的反气旋和旋风涡流中的能量消散。这些观察结果揭示了高水平的湍流，其中陡峭和粗糙的地形坡度改变了与特别是反气旋涡旋有关的加剧的北向流动。在底部附近和中深度（200–800 m）都观察到了较高的耗散。近壁面湍流发生在突出的陡坡的背风处，弗洛德数的增加表明水力控制。能量也以向上传播的内部波的形式辐射。在中深度的高耗散发生在强烈的垂直剪切区域，那里的地形坡度改变了北涡流的垂直结构。在这里，较低的理查森数和势涡（PV）的等密度梯度的局部变化表明，较高的耗散与水平剪切不稳定性有关。流动的地形转向也引起了中深层消散的增加。这导致了较大的反气旋涡度，并在地形坡度附近产生负PV，这表明离心力不稳定是耗散的局部增强。