POM模式在日本南部黑潮路径变异研究中的应用

日本南部黑潮路径变异对北太平洋地区的气候和环境具有显著的影响,对黑潮路径变异的研究具有重要的意义。本文利用POM(Princeton Ocean Model)数值模式模拟了日本南部黑潮的路径变异情况,分析了黑潮大弯曲路径形成的可能机制。研究结果表明,当黑潮处于非大弯曲路径时,相对位势涡度的平均值呈现递减趋势,说明日本南部低位势涡度水在不断积累,这样会使得四国再循环流的强度增强,迫使黑潮保持平直路径,同时,近岸黑潮垂直流速剪切增大,斜压不稳定性的作用也逐渐增大;当黑潮从非大弯曲路径向大弯曲路径过渡时,再循环流强度的减弱会导致黑潮的流速剪切减小。根据海表高度异常场以及海洋上层流场信息发现,近岸黑潮附近的气旋涡会随着再循环流区域反气旋涡的东侧向南运动,最终导致黑潮大弯曲的发生。分析涡流的能量,结果显示,黑潮大弯曲路径的形成与斜压不稳定性密切相关。

Application of the POM model to study the path variations of Kuroshio currents in southern Japan seas

Path variations of the Kuroshio currents in the southern Japan seas have a significant impact on the climate and environment. In this study, we used the Princeton Ocean Model (POM) to simulate the Kuroshio path variations south of Japan, and analyzed the formation mechanism of the Kuroshio large meander events. The results show a decreasing trend of the average relative vorticity when the Kuroshio is taken as the non-large path, indicating an accumulation of the low potential vorticity (PV) south of Japan which intensified the strength of the Shikoku recirculation gyre, thereby forcing the Kuroshio into its straight path. Meanwhile, the vertical velocity shear of the alongshore Kuroshio was increasing, and the impact of the baroclinic instability was also gradually increasing. During the transition period from the Kuroshio non-large meander to the large meander, a sudden release of velocity shear corresponded well to the weakening of the Shikoku recirculation gyre. According to the sea surface height (SSH) anomaly fields and the mean velocity field in the upper ocean, we found that the cyclonic eddy around the offshore Kuroshio moved southward, carried by a southward flow in the eastern part of the anticyclonic eddy in the region of the Shikoku recirculation gyre. This led to the eventual development of the Kuroshio large meander. The results of our eddy energetic analysis indicate that the formation of the Kuroshio large meander is closely associated with baroclinic instability.