The land‐sea breeze is resonant with the inertial response of the ocean at the critical latitude of 30°N/S. 1‐D vertical numerical experiments were undertaken to study the key drivers of enhanced diapycnal mixing in coastal upwelling systems driven by diurnal‐inertial resonance near the critical latitude. The effect of the land boundary was implicitly included in the model through the “Craig approximation” for first‐order cross‐shore surface elevation gradient response. The model indicates that for shallow water depths (<∼100 m), bottom shear stresses must be accounted for in the formulation of the “Craig approximation,” as they serve to enhance the cross‐shore surface elevation gradient response, while reducing shear and mixing at the thermocline. The model was able to predict the observed temperature and current features during an upwelling/mixing event in 60 m water depth in St Helena Bay (∼32.5°S, southern Benguela), indicating that the locally forced response to the land‐sea breeze is a key driver of diapycnal mixing over the event. Alignment of the subinertial Ekman transport with the surface inertial oscillation produces shear spikes at the diurnal‐inertial frequency; however their impact on mixing is secondary when compared with the diurnal‐inertial resonance phenomenon. The amplitude of the diurnal anticyclonic rotary component of the wind stress represents a good diagnostic for the prediction of diapycnal mixing due to diurnal‐inertial resonance. The local enhancement of this quantity over St Helena Bay provides strong evidence for the importance of the land‐sea breeze in contributing to primary production in this region through nutrient enrichment of the surface layer.

中文翻译：

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昼间惯性驱动的海岸上升流系统的增强垂直混合：数值实验

在30°N / S的临界纬度下，陆海风与海洋的惯性响应产生共振。进行了一维垂直数值实验，研究了由临界纬度附近的昼间惯性共振驱动的沿海上升流系统中辉岩混合增强的关键驱动力。对于一阶跨岸表面海拔梯度响应，通过“克雷格近似”将土地边界的影响隐含在模型中。该模型表明对于浅水深度（< 〜100 m），必须在“克雷格近似”的公式中考虑底部剪应力，因为它们可增强跨岸表面海拔梯度响应，同时减少在热跃线处的剪切和混合。该模型能够预测圣海伦娜湾60 m水深处的上升流/混合事件期间观测到的温度和当前特征（〜32.5°S，Benguela南部），表明当地对陆海风的强迫反应是该事件中泛辉混合的主要驱动因素。亚惯性埃克曼输运与表面惯性振荡的对准会在日惯性频率上产生剪切峰值。然而，与昼间惯性共振现象相比，它们对混合的影响是次要的。风的昼夜反气旋旋转分量的振幅代表了对昼夜惯性共振引起的泛辉混合的预测的良好诊断。在圣赫勒拿湾上，这一数量的局部增加为陆海风通过表层养分的富集对该区域的初级生产做出贡献的重要性提供了有力的证据。