海洋科学学术讲座预告第383期：Preliminary Study of the Interaction between Open Ocean and Marginal Sea on Decadal to Multidecadal Timescales 开阔洋与边缘海相互作用年代际变化的初步研究

报告内容简介：

      The sea level in the east of Luzon Strait along the latitudinal band (18o-22oN, 125o-170oE) demonstrates a unique decreasing trend during 1993-2020, with weakening of eddy kinetic energy (EKE), weaker Kuroshio transport and stronger looping pathway in the Luzon Strait. Neither the surface wind forcing (remote Rossby wave and local Ekman convergence/divergence) nor surface buoyancy forcing (heat flux and Ekman thermal advection) could explain the observed sea level and EKE decreasing trend. From the subsurface perspective, by using the observational data analysis and ventilated thermocline theory, we propose that the reduction of mode water in the subsurface ocean contributes to the above changes during the past ~30 years. When the volume of mode water shrinks, the slope of thermocline would flatten, making the upper thermocline lift along the Luzon Strait latitudinal band. Whereafter, the subtropical front weakens, reducing the vertical velocity shear between the surface eastward Subtropical Counter Current and subsurface westward North Equatorial Current and sea level due to the baroclinic adjustment. Besides, the flattened thermocline and weakened vertical velocity shear results in the EKE reduction, which will contribute to the decreasing of sea level due to the weakened eddy-forcing. Furthermore, due to the weakening of the Kuroshio in the Luzon Strait since 1990s, the Kuroshio shows an enhanced looping path in the Northeastern South China Sea (NE-SCS), inducing stronger EKE in this region. Analysis confirms that the energy transfer by baroclinic instability is dominant for the increasing of EKE. This study provides insight into the interaction between marginal sea (i.e., the SCS) and open ocean (i.e., the western Pacific Ocean), finally linking to the global climate change.

      1993-2020年间，吕宋海峡东部沿纬度带（18o-22oN、125o-170oE）海平面呈现出独特的条带状下降趋势，伴随涡动能（EKE）减弱，黑潮输送减弱 。 表面风强迫和表面浮力强迫都无法解释观测到的海平面和 EKE下降趋势。 通过观测数据分析和通风温跃层理论，我们提出过去~30年中次表层海洋模态水的减少导致了上述变化。 指出最近几十年全球变暖和AMO正位相共同作用，导致模态水体积收缩，温跃层的斜率会变平，使得上温跃层沿吕宋海峡纬度带向上抬升。随后，由于斜压调整，副热带锋面减弱，海表面东向的副热带逆流和次表层西向的北赤道流之间的垂向速度剪切减弱，使得海表面条带状下降趋势。此外，平缓的温跃层和减弱的垂向速度剪切带来的EKE的减小将进一步导致海平面下降。本研究对深入了解边缘海和开阔大洋间相互作用及其与气候变化之间的联系带来了新的视角。.