ABSTRACT

The importance of explicitly resolving the Stokes drift in ocean surface drift modelling is demonstrated by comparing four models with 58,612 observational data points obtained from undrogued drifting buoys in the Estuary and Gulf of St. Lawrence, Canada. Drift model inputs are obtained from regional atmosphere and ocean circulation, and spectral wave models. The control drift model considers near-surface currents provided by the top grid cell of the ocean circulation model, which is 5-m thick, and a correction term proportional to the near-surface wind. The three other drift models account for the unresolved near-surface current shear by extrapolating the near-surface currents to the surface assuming Ekman dynamics. Two of these models consider explicitly the Stokes drift, with and without a wind correction term. Proposed models reduce the mean separation distance between observed and predicted trajectories by 34–40% relative to the control model, on average, for forecast times ranging from 3 to 72 h. The best improvement with respect to all metrics used is, however, obtained for the model that takes into account the near-surface shear correction and the Stokes drift, without any wind correction term (skill score of 0.93 after 3 h and 0.81 after 72 h).

摘要

通过将四个模型与从加拿大河口和圣劳伦斯湾的无绳漂流浮标获得的 58,612 个观测数据点进行比较，证明了在海洋表面漂移建模中明确解决斯托克斯漂移的重要性。漂移模型输入来自区域大气和海洋环流以及光谱波模型。控制漂移模型考虑了由海洋环流模型顶部网格单元提供的近地表流，其厚度为 5 米，以及与近地表风成比例的校正项。假设 Ekman 动力学，其他三个漂移模型通过将近地表电流外推到地表来解释未解决的近地表电流剪切。其中两个模型明确考虑了斯托克斯漂移，有和没有风修正项。对于 3 到 72 小时的预测时间，相对于控制模型，所提出的模型将观测轨迹和预测轨迹之间的平均间隔距离平均减少了 34-40%。然而，对于所使用的所有指标而言，最好的改进是在考虑了近地表剪切修正和斯托克斯漂移的模型中获得的，没有任何风修正项（3 小时后的技能得分为 0.93，72 小时后为 0.81 ）。