Numerical Analysis of Green Island Wake Due to Passing of Kuroshio

Abstract

Kuroshio-induced island wake downstream the Green Island, Taiwan due to passing of Kuroshio is studied using satellite imagery, in-situ measurements, and a depth-averaged shallow-water model. Both a circular island and real Green Island are employed to study the effect of geometry on the island wake characteristics. It is found that the irregular geometry has a significant effect on the flow field and vortex downstream, especially for flow field near the island. Spatial scales, such as the aspect ratio and dimensionless width, temporal scale represented by Strouhal number as well as the relative propagation speed of the vortices are quantified. It is found that the aspect ratio is between 1.76 and 2.72 from satellite images and between 2.77 and 2.99 from numerical simulations. The dimensionless width is in the range of 1.84 and 1.92 from satellite images, and 1.45 and 1.80 from numerical modelling. The Strouhal number varies from 0.13 to 0.17 from numerical simulations. Magnitude of the propagation speed of the vortices is about a half of the Kuroshio speed, implying that the nonlinearity as well as interactions of vortices and the Kuroshio are strong.