The present study aims to estimate effective diahaline turbulent salinity fluxes and diffusivities in numerical model simulations of estuarine scenarios. The underlying method is based on a quantification of salinity mixing per salinity class, which is shown to be twice the turbulent salinity transport across the respective isohaline. Using this relation, the recently derived universal law of estuarine mixing, predicting that average mixing per salinity class is twice the respective salinity times the river run‐off, can be directly derived. The turbulent salinity transport is accurately decomposed into physical (due to the turbulence closure) and numerical (due to truncation errors of the salinity advection scheme) contributions. The effective diahaline diffusivity representative for a salinity class and an estuarine region results as the ratio of the diahaline turbulent salinity transport and the respective (negative) salinity gradient, both integrated over the isohaline area in that region and averaged over a specified period. With this approach, the physical (or numerical) diffusivities are calculated as half of the product of physical (or numerical) mixing and the isohaline volume, divided by the square of the isohaline area. The method for accurately calculating physical and numerical diahaline diffusivities is tested and demonstrated for a three‐dimensional idealized exponential estuary. As a major product of this study, maps of the spatial distribution of the effective diahaline diffusivities are shown for the model estuary.

中文翻译：

---

河口中的有效盐扩散率

本研究的目的是在河口情景的数值模拟中估计有效的盐度湍流盐度通量和扩散率。基本的方法基于每个盐度类别的盐度混合的定量，这显示为在各个异卤中的湍流盐度迁移的两倍。利用这种关系，可以直接推导出最近推导出的河口混合规律，它预测每个盐度等级的平均混合量是各自盐度乘以河流径流的两倍。湍流盐度传输被精确地分解为物理（由于湍流闭合）和数值（由于盐度对流方案的截断误差）贡献。代表盐度等级和河口区域的有效盐度扩散率是由该盐度湍流盐度迁移率和相应的（负）盐度梯度之比得出的，二者在该区域的等盐度区域上积分并在指定时期内取平均值。使用这种方法，物理（或数值）扩散率计算为物理（或数值）混合和等卤体积的乘积的一半，再除以等卤面积的平方。对三维理想化的指数河口测试并演示了用于精确计算物理和数值二苯胺扩散率的方法。作为这项研究的主要产品，显示了模型河口有效二苯胺扩散率的空间分布图。