Abstract The alongshore subtidal water circulation along the South Portugal inner shelf is characterized by the temporal alternation of equatorward (i.e., broadly eastward) flows related to coastal upwelling processes and poleward (i.e., broadly westward) Coastal Counter Currents (CCCs). The objective of this study is to get insights about the main drivers of CCCs based on kinematic parameters describing the structure of the flow at the moment it changes direction. The parameters are derived from an extensive bottom-mounted ADCP dataset (16 deployments; 34,121 hourly records) collected at a single mooring (23 m water depth). Results show that the so-called incipient flows present contrasted general patterns whether they turn from equatorward to poleward or the opposite. Complementary observations at a nearby station indicate that these characteristics are spatially consistent along the studied area. Although 70% of CCCs are generated under favourable wind conditions (Levanter), these flows generally develop through the bed layer, in particular in summer. Hence, the Levanter wind - expected to promote flow setup through the surface layer - is not the main driver of CCCs in most cases. The general structure of incipient CCCs strongly suggests that the dominant force competing with the wind stress is an alongshore pressure gradient (APG). Furthermore, the maximum equatorward flow magnitude before CCCs setup is significantly correlated with the following (poleward) acceleration of incipient CCCs near the bed. Such relation is consistent with the development of CCCs due to the unbalance of an APG (produced during active upwelling) when wind relaxes. This process is further supported by an analysis of the depth-averaged momentum equation which suggests that the coastal circulation is mainly driven by linear dynamics in the region.

中文翻译：

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葡萄牙南部初期沿海逆流的结构作为其强迫因子的指标

摘要 沿葡萄牙南部内陆架的沿岸潮下带水循环的特点是与沿海上升流过程相关的赤道（即大致向东）流动和向极（即大致向西）海岸逆流（CCC）的时间交替。本研究的目的是根据描述流动结构改变方向时的运动学参数，深入了解 CCC 的主要驱动因素。这些参数来自广泛的底部安装的 ADCP 数据集（16 次部署；34,121 小时记录）在单个系泊处（23 m 水深）收集。结果表明，所谓的初期流动呈现出对比鲜明的一般模式，无论它们是从赤道转向极地还是相反。附近站点的补充观测表明，这些特征沿研究区域在空间上是一致的。尽管 70% 的 CCC 是在有利的风力条件下（Levanter）产生的，但这些流动通常通过床层发展，尤其是在夏季。因此，在大多数情况下，Levanter 风 - 预计会促进通过表层的流动设置 - 不是 CCC 的主要驱动力。初期 CCC 的一般结构强烈表明，与风应力竞争的主导力是沿岸压力梯度 (APG)。此外，在 CCC 设置之前的最大赤道流幅度与床附近初始 CCC 的以下（极向）加速度显着相关。这种关系与风减弱时 APG（主动上升流期间产生）的不平衡导致 CCC 的发展是一致的。对深度平均动量方程的分析进一步支持了这一过程，这表明沿海环流主要由该地区的线性动力学驱动。