New Insight Into the Onshore Intrusion of the Kuroshio Into the East China Sea

The Kuroshio Current, a vigorous western boundary current in the Pacific, is responsible for bringing high temperature, high salinity, and phosphate-rich open ocean water into the East China Sea (ECS) when it flows past Taiwan and generates a branch current, known as the Kuroshio Branch Current (KBC), which intrudes onto the continental shelf of the ECS. Based on observations and numerical modeling, a 1.5-layer reduced-gravity model is evaluated and modified to simulate the flow pattern of the Kuroshio intrusion (KI) northeast of Taiwan. We revised the analytical solution derived by Hsueh (1992), to conserve the horizontal momentum balance in the along-shelf and cross-shelf directions. The new analytical solution not only explains the KI angle but also addresses the KBC recirculation mechanism. To sustain the steady-state momentum balance in the area adjacent to the shelf break northeast of Taiwan, there must be a recirculation that plays the same role in vorticity dynamics as the combination of the joint effect of baroclinicity and relief, bottom friction, and nonlinear advection. Unlike previous studies, our results agree well with the observations and could account for seasonal variations in the KI direction. Moreover, the new model predicts a reasonable velocity maximum (0.42 m s(-1)) over the shelf break. Satellite data and numerical results confirm that the new solution reflects a reasonable estimation for KI direction. This theory may potentially be applied to regions with trenches or valleys with completely different flow patterns by using similar analytical methods.

Automated summary

A modified analytical solution was developed to simulate the flow pattern of the Kuroshio intrusion northeast of Taiwan, maintaining horizontal momentum balance. The new model accurately predicts the direction of the Kuroshio intrusion and aligns well with observational data, offering potential applications in regions with different flow patterns.