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首页> 外文期刊>Journal of Physical Oceanography >The Impact of a Variable Mixing Efficiency on the Abyssal Overturning
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The Impact of a Variable Mixing Efficiency on the Abyssal Overturning

机译：可变混合效率对深层倾覆的影响

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In studies of ocean mixing, it is generally assumed that small-scale turbulent overturns lose 15%-20% of their energy in eroding the background stratification. Accumulating evidence that this energy fraction, or mixing efficiency R-f, significantly varies depending on flow properties challenges this assumption, however. Here, the authors examine the implications of a varying mixing efficiency for ocean energetics and deep-water mass transformation. Combining current parameterizations of internal wave-driven mixing with a recent model expressing R-f as a function of a turbulence intensity parameter Re-b = epsilon(nu)u N-2, the ratio of dissipation epsilon(nu) to stratification N-2 and molecular viscosity nu, it is shown that accounting for reduced mixing efficiencies in regions of weak stratification or energetic turbulence (high Re-b) strongly limits the ability of breaking internal waves to supply oceanic potential energy and drive abyssal upwelling. Moving from a fixed R-f = 1/6 to a variable efficiency R-f(Re-b) causes Antarctic Bottom Water upwelling induced by locally dissipating internal tides and lee waves to fall from 9 to 4 Sverdrups (Sv; 1 Sv equivalent to 10(6) m(3) s(-1)) and the corresponding potential energy source to plunge from 97 to 44 GW. When adding the contribution of remotely dissipating internal tides under idealized distributions of energy dissipation, the total rate of Antarctic Bottom Water upwelling is reduced by about a factor of 2, reaching 5-15 Sv, compared to 10-33 Sv for a fixed efficiency. The results suggest that distributed mixing, overflow-related boundary processes, and geothermal heating are more effective in consuming abyssal waters than topographically enhanced mixing by breaking internal waves. These calculations also point to the importance of accurately constraining R-f (Re-b) and including the effect in ocean models.
机译：在海洋混合研究中，通常认为小规模的湍流倾覆会侵蚀背景分层，从而损失其能量的15％-20％。越来越多的证据表明，这种能量分数或混合效率R-f会根据流动特性而显着变化，这对这一假设提出了挑战。在这里，作者研究了混合能效变化对海洋能量学和深水物质转化的影响。将内部波驱动混合的当前参数化与将Rf表示为湍流强度参数Re-b = epsilon（nu）/ nu N-2，耗散epsilon（nu）与分层N-2之比的函数的最新模型相结合以及分子黏度nu，表明在弱分层或高能湍流（高Re-b）区域中降低混合效率的原因强烈地限制了破坏内部波浪提供海洋势能并驱动深渊上升的能力。从固定Rf = 1/6变为可变效率Rf（Re-b）会导致南极底潮由局部耗散的内部潮汐和Lee波引起的上升流从9降到4 Sverdrups（Sv; 1 Sv等于10（6） ）m（3）s（-1））和相应的潜在能源从97 GW降至44 GW。当在理想的能量耗散分布下增加内部消散潮汐的贡献时，南极海底上升流的总速率降低了约2倍，达到5-15 Sv，而固定效率为10-33 Sv。结果表明，分散混合，与溢流相关的边界过程和地热加热比深水通过破坏内部波浪来增强混合比消耗深海水更有效。这些计算还指出了精确约束R-f（Re-b）并将其纳入海洋模型的重要性。

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