ABSTRACT

Predictions of drift trajectories based on four drift models were compared with observations from drifting buoys deployed in 2014 and 2015 in the Estuary and Gulf of St. Lawrence to show the impact of the current vertical shear on the surface drift predictions. Input of ocean currents and winds are obtained from ISMER's 5 km resolution ocean circulation model and from the Canadian Regional Deterministic Prediction System, respectively. The control drift model A considers depth-averaged near-surface currents (0–5 m) provided by the top grid cell of the ocean circulation model. Model B performs a linear extrapolation assuming a constant vertical shear equal to that between the first two cells of the ocean model. Models C and D perform a dynamic extrapolation assuming an Ekman layer with a constant or linearly increasing vertical viscosity, respectively. Model performance is evaluated based on several error metrics. Drift models based on extrapolated surface currents reduce separation distances relative to the control model by 25% (model B), 31% (model C) and 35% (model D) on average, for lead times from 3 h to 72 h. We thus recommend the use of extrapolation methods of near-surface ocean currents for improving surface drift forecasting skills in support of emergency response.

摘要

将基于四个漂移模型的漂移轨迹预测与2014年和2015年在河口和圣劳伦斯湾部署的浮标的观测结果进行比较，以显示当前垂直剪切对地表漂移预测的影响。洋流和风的输入分别从ISMER的5 km分辨率海洋环流模型和加拿大区域确定性预测系统获得。控制漂移模型A考虑了海洋环流模型顶部网格提供的深度平均近地表水流（0-5 m）。模型B进行线性外推，假设恒定的垂直剪切力等于海洋模型的前两个单元之间的垂直剪切力。模型C和D进行动态外推，假设埃克曼层的垂直粘度恒定或线性增加，分别。基于几个错误指标评估模型性能。基于外推表面电流的漂移模型将相对于控制模型的分离距离平均缩短了25％（模型B），31％（模型C）和35％（模型D），交货时间为3小时到72小时。因此，我们建议使用近地洋流的外推方法来提高地表漂移预报技能，以支持应急响应。