Abstract A set of realistic coastal coupled ocean-wave numerical simulations is used to study the impact of surface gravity waves on a tidal temperature front and surface currents. The processes at play are elucidated through analyses of the budgets of the horizontal momentum, the temperature, and the turbulence closure equations. The numerical system consists of a 3D coastal hydrodynamic circulation model (Model for Applications at Regional Scale, MARS3D) and the third generation wave model WAVEWATCH III (WW3) coupled with OASIS-MCT at horizontal resolutions of 500 and 1500 m, respectively. The models were run for a period of low to moderate southwesterly winds as observed during the Front de Maree Variable (FroMVar) field campaign in the Iroise Sea where a seasonal small-scale tidal sea surface temperature front is present. Over the 2 day period considered, long fetch waves grow gradually propagating north east and east. Contrasting a stand-alone ocean run with a coupled ocean-wave run shows that waves move the Ushant front offshore by up to 4 kilometres and cool the offshore stratified side of the front by up to 1.5°C. The analysis of the temperature budget shows that the change in advection is the dominant factor contributing to the frontal shift while the contribution of wave enhanced vertical temperature diffusion is secondary. Temperature, considered to be a tracer, is advected in the coupled run by the Lagrangian current resulting from the quasi-Eulerian and Stokes drift. Although the Stokes drift is directed shorewards, changes in the quasi-Eulerian current lead to a more offshore advection in the coupled than the stand-alone run. The quasi-Eulerian current is reduced (enhanced) during the ebb (flood) flow which correspond to periods of wave-following (-opposing) currents. This is due to wave breaking enhanced vertical mixing acting on the positive vertical gradient present in the quasi-Eulerian current during both ebb and flood tides. Partially coupled runs reveal that it is the surface flux of TKE associated to wave breaking that is key rather than the changes in the surface stress. They further elucidate the role of other modelled wave related processes. Although the contribution of the Stokes–Coriolis force and the wave breaking induced enhancement in vertical mixing to the quasi-Eulerian current are of similar magnitude and sign, it does not contribute significantly to the frontal shift. This is because it partially counters the Stokes drift advection which pushes the front shorewards. All Stokes drift related processes combined thus only lead to a very slight displacement of the front.

中文翻译：

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表面重力波对潮汐锋的影响：耦合模型透视

摘要 利用一组真实的海岸耦合海浪数值模拟来研究表面重力波对潮汐温度前沿和表面流的影响。通过对水平动量、温度和湍流闭合方程的预算分析，阐明了这些过程。数值系统由 3D 沿海水动力循环模型（区域尺度应用模型，MARS3D）和第三代波浪模型 WAVEWATCH III (WW3) 与 OASIS-MCT 耦合，水平分辨率分别为 500 和 1500 m。这些模型运行了一段时间的低到中等西南风，如在 Iroise 海的 Front de Maree Variable (FroMVar) 野外活动期间观察到的那样，其中存在季节性小规模潮汐海面温度锋。在考虑的 2 天期间，长波逐渐向东北和向东传播。将独立的海洋运行与耦合的海浪运行进行对比表明，海浪将 Ushant 锋向近海移动了 4 公里，并使锋的离岸分层侧冷却高达 1.5°C。温度收支分析表明，平流变化是导致锋面偏移的主要因素，而波浪增强垂直温度扩散的贡献是次要的。被认为是示踪物的温度在由准欧拉和斯托克斯漂移产生的拉格朗日电流的耦合运行中被平流。尽管斯托克斯漂移是指向岸边的，但准欧拉洋流的变化导致耦合中比独立运行更多的离岸平流。准欧拉电流在退潮（洪水）流动期间减少（增强），这对应于波浪跟随（反向）电流的周期。这是由于波浪破碎增强的垂直混合作用于退潮和洪水期间准欧拉洋流中存在的正垂直梯度。部分耦合的运行表明，与波浪破碎相关的 TKE 的表面通量是关键，而不是表面应力的变化。他们进一步阐明了其他建模波相关过程的作用。尽管斯托克斯-科里奥利力的贡献和垂直混合中的波浪破碎诱导增强对准欧拉电流具有相似的幅度和符号，但它对锋移没有显着贡献。这是因为它部分抵消了将锋面推向海岸的斯托克斯漂移平流。因此，所有与斯托克斯漂移相关的过程结合在一起只会导致前部的非常轻微的位移。