Studies on the Interaction between North Pacific Intermediate Water and the Kuroshio

我们假设，产生NPIW的亚北极到副热带环流的交叉环流输送的变化导致了黑潮/黑潮伸展洋流系统的长期变化。为了验证这一假说并探测实际发生的NPIW的形成过程，我们进行了数据分析、数值实验和野外观测，取得了不同寻常的结果。(1)基于CTD/LADCP观测的四次水团和洋流观测，我们揭示了约10Sv的横涡Oyashio输送是通过以下两个过程进行的：沿西部边界的直接横涡输送和沿近海SAF发生的由于等周期混合而发生的跨次北极锋(SAF)过程。(2)用具有真实地形和年平均风…的允许涡动的三层数值模式，真实地再现了西边界流穿过风生涡旋边界的侵入和相关的交叉涡旋输送。更多的压力，特别是向南侵入的Oyashio和北太平洋中间水(NPIW)的形成。由千岛群岛强潮混合产生的模式昼夜上升流中，约有3SV引起经向-昼夜翻转环流。这些结果解释了观测到的沿西边界的约4Sv的横涡Oyashio输送参与了NPIW的形成。(3)利用CTD/TRAVED-CTD(MVP：Moving Vent Profiler)和LADCP/ADCP对黑潮延伸段进行了高分辨率密集观测。这些观测表明，波长约200公里的中深度锋面波以0.2m/S的相速度沿下游传播，放大了幅度。直到东经150时，海浪在下游地区非常有效地分解并混合了这两个水团。线性稳定性分析表明，由于表层涡度异常与中深度涡度异常的耦合，观测到的锋面波可能是斜压不稳定波。因此，Oyashio水通过进入黑潮延伸区，加强了强烈混合和NPIW的形成。较少

We here hypothesize that variation of the cross-gyre transport from the subarctic to subtropical gyres producing NPIW induces long-term variations in the Kuroshio/Kuroshio Extension current system. In order to validate this hypothesis and detect the actually occurring formation processes of NPIW, we conducted data-analysis, numerical experiments and field observations; we successfully obtained extraordinary results. (1) Based on four surveys of water masses and ocean currents using CTD/LADCP observation, we revealed about 10Sv of cross-gyre Oyashio transport through the following two processes : direct cross-gyre transport along the western boundary and cross-subarctic front (SAF) process occurring along the offshore SAF due to isopycnal mixing. (2) The intrusion of western boundary currents across the wind-driven gyre boundary and related cross-gyre transport are realistically reproduced with a eddy-permitting three layer numerical models with realistic topography and annual mean wind … More stress, with special emphasis on the Oyashio southward intrusion and North Pacific intermediate Water (NPIW) formation. About 3Sv of the model diapycnal upwelling occurring due to strong tidal mixing along the Kurii islands induces a meridional-diapycnal overturning circulation. These results explain the observed features that about 4Sv of the cross-gyre Oyashio transport along the western boundary participate in the formation of NPIW. (3) High-resolution intensive observation using CTD/towed-CTD (MVP : Moving Vessel Profiler) and LADCP/ADCP were performed around the Kuroshio Extension. These observations revealed that intermediate-depth frontal waves with the wavelength of about 200km propagate in the downstream direction with the phase speed of 0.2m/s, amplifying the amplitude. The waves break down and mix the two water masses very efficiently in the downstream regions until 150E. A linear stability analysis reveals that the observed frontal waves are possibly the baroclinically unstable waves due to the coupling between the surface and intermediate-depth vorticity anomalies. The Oyashio water thus enhances intensive mixing and NPIW formation by entering into the Kuroshio Extension. Less