In the northeastern tropical Atlantic, a region of high potential vorticity (PV) determines the size of the exchange window for the interior thermocline flow of the subtropical cell via its variations in strength and extent. Variability of this PV barrier has the potential to impact the ventilation of the tropical Atlantic on decadal timescales. Here, the impact of the North Atlantic Oscillation (NAO) on the PV barrier related to isopycnals within the thermocline of the subtropical-tropical Atlantic Ocean is assessed from Argo observations for the time period of 2006–2022. Relative to the negative NAO phase (2009–2010), during the positive NAO phase (2014–2019), the North Atlantic subtropical high and the northeast trades are intensified. Satellite-derived wind stress curl shows increased upwelling/downwelling on the equatorward/poleward side of the trade wind zone, respectively. In the subtropical-tropical Atlantic, a symmetric pattern of isopycnal heave is observed: rising isopycnals within 20°N and 20°S and sinking poleward of that. With rising isopycnals, the PV barrier in the northeastern tropical Atlantic becomes stronger. Analyses of geostrophic velocities and the Sverdrup streamfunction show that during the positive NAO phase there are increased equatorward velocities at thermocline level along the western boundary and reduced velocities through the interior as a result of intensified northeast trades and therefore a strengthened PV barrier. Intensified trades lead to enhanced subduction of thermocline waters and, independent of that, to a strengthened Equatorial Undercurrent transport as observed at the mooring site at 0°, 23°W, likely via the pulling effect of the subtropical cells.

中文翻译：

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北大西洋涛动对上副热带-热带大西洋年代际变化的影响

在热带大西洋东北部，高位涡（PV）区域通过其强度和范围的变化决定了副热带环流内部温跃层流的交换窗口的大小。这种光伏屏障的变化有可能在十年时间尺度上影响热带大西洋的通风。在此，根据 2006 年至 2022 年期间的 Argo 观测评估了北大西洋涛动 (NAO) 对与副热带-热带大西洋温跃层内等重线相关的光伏屏障的影响。相对于负NAO阶段（2009-2010年），在NAO正阶段（2014-2019年），北大西洋副热带高压和东北部贸易增强。卫星产生的风应力旋度显示信风区赤道侧/极地侧的上升流/下降流分别增加。在副热带-热带大西洋，观察到等重线隆起的对称模式：等重线在 20°N 和 20°S 范围内上升，向极地方向下沉。随着等密度的增加，热带大西洋东北部的光伏屏障变得更强。对地转速度和斯维尔德鲁普流函数的分析表明，在正 NAO 阶段，由于东北贸易的加剧以及光伏壁垒的加强，沿西部边界的温跃层水平的赤道速度增加，而通过内部的速度减少。贸易的加强导致温跃层水域的俯冲增强，并且与此无关，如在西经 0°、23° 的系泊地点观察到的那样，可能通过副热带细胞的拉力效应，导致赤道暗流输送的加强。