The eddy diffusivity in the ocean pycnocline \(K_{N} = \gamma {\varepsilon \mathord{\left/ {\vphantom {\varepsilon {N^{2} }}} \right. \kern-\nulldelimiterspace} {N^{2} }}\) is analyzed based on field measurements of the turbulent kinetic energy (TKE) dissipation rate \(\varepsilon \left( z \right)\) and buoyancy frequency \(N\left( z \right)\) profiles and an assumed mixing efficiency of \(\gamma = 0.2\). The microstructure measurements were taken between 2013 and 2019 in various regions of the Bay of Bengal (BoB) as well as the central Gulf Stream (GS) and deep waters of the Southern California Bight (SCB). The space–time variability of \(K_{N} \left( {z,t} \right)\) observed in the pycnocline of the southeastern BoB is likely related to internal-wave generated turbulence, identified by its following of MacKinnon–Gregg scaling (MacKinnon and Gregg in J Phys Oceanogr 33(7):1476–1492, 2003). The probability distribution function of diffusivity \({{CDF}}\left( {K_{N} } \right)\) could be well fitted by generalized extreme value distribution (GEVD) for all regions of BoB and other oceans. Mixing rates in the upper pycnocline of BoB during extended southwestern monsoon period tend to be larger in the southern parts of the Bay compared to central and northern parts. Statistics of \(K_{N}\) in the GS and SCB waters appear to be similar to those in the southern BoB with a characteristic median value ~ \(2 \times 10^{ - 6}\) m²/s, suggesting relatively low intensity of vertical mixing therein compared to the canonical pycnocline diffusivity of \(K_{N} \approx 10^{ - 5}\) m²/s.

海洋重跃层中的涡流扩散系数\(K_{N} = \gamma {\varepsilon \mathord{\left/ {\vphantom {\varepsilon {N^{2} }}} \right. \kern-\nulldelimiterspace} { N^{2} }}\)的分析基于湍动能 (TKE) 耗散率\(\varepsilon \left( z \right)\)和浮力频率\(N\left( z \right ) )\)配置文件和假设的混合效率\(\gamma = 0.2\)。微观结构测量是在 2013 年至 2019 年间在孟加拉湾 (BoB) 的各个区域以及墨西哥湾流中部 (GS) 和南加州湾 (SCB) 的深水区进行的。\(K_{N} \left( {z,t} \right)\)的时空变异性在 BoB 东南部的重跃层中观察到的可能与内波产生的湍流有关，通过其 MacKinnon-Gregg 标度确定（MacKinnon 和 Gregg in J Phys Oceanogr 33(7):1476-1492, 2003）。扩散系数的概率分布函数\({{CDF}}\left( {K_{N} } \right)\)可以通过广义极值分布 (GEVD) 很好地拟合 BoB 和其他海洋的所有区域。与中部和北部相比，在西南季风延长期间，BoB 上部重跃层的混合率在海湾南部往往更大。GS 和 SCB 水域的\(K_{N}\)统计数据似乎与 BoB 南部的统计数据相似，具有特征中值 ~  \(2 \times 10^{ - 6}\) m^{2 /s，表明与}\(K_{N} \约10^{ - 5}\) m ² /s的典型重跃层扩散率相比，其中的垂直混合强度相对较低。