In this note, we provide an overview of the theoretical, numerical, and observational studies focused on oceanic eddy diffusivity, with an emphasis on double-diffusive convection (DDC). DDC, when calculated using the turbulent kinetic energy (TKE) equation, produces a negative diffusion of density. A second-moment closure model shows that DDC is effective within a narrow range. Other parameterizations can use in the actual sea, but improvements are still needed. Mixing coefficients referring to mixing efficiency are key factors when distinguishing DDC from conventional turbulence. Here, we show that measurements involving the gradient Richardson number, the buoyancy Reynolds number, and density ratio play a crucial role in determining eddy diffusivity in the presence of DDC. Therefore, deployment of a microstructure profiler together with either an acoustic Doppler current profiler (ADCP), lowered ADCP, or electromagnetic current meter is essential when measuring eddy diffusivity in the ocean’s interior.

中文翻译：

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关于估算大洋双扩散对流涡扩散系数的一个注记

在本说明中，我们概述了侧重于海洋涡流扩散的理论、数值和观测研究，重点是双扩散对流 (DDC)。DDC，当使用湍流动能 (TKE) 方程计算时，会产生密度的负扩散。二阶矩闭合模型表明 DDC 在较窄的范围内是有效的。其他参数化可以在实际海中使用，但仍需要改进。与混合效率相关的混合系数是区分 DDC 与传统湍流的关键因素。在这里，我们表明涉及梯度理查森数、浮力雷诺数和密度比的测量在确定存在 DDC 的涡流扩散率方面起着至关重要的作用。所以，