Evolution of the Kuroshio-Induced Island Wake: Satellite Observations and Numerical Simulation

Previous results of satellite imagery analysis and in-situ observations in the Green Island wake, southeast of Taiwan, consistent with the characteristics of the von Kármán vortex street. However, the difficulty in studying a wake is the lack of simultaneous large-area surveys capturing its entire horizontal structure and dynamics process. Besides, the actual wake is variable, but wake described by a numerical model is basically ideal. The Himawari satellite data with high temporal and spatial resolution captured the process of wake development, a breakthrough in island-wake dynamics, eliminating the difficult problem of measuring large areas simultaneously.

In this study, the incoming flow velocity of the wake were be estimated by the maximum cross correlation method using SST data, and the SST wakes pattern captured the continually process of wake, including wake alone, wake with a tail stretching downstream, a S-shaped meandering wake, and wake with a small cyclonic cold core but no tail stretching downstream. In addition, The MITgcm numerical model used to employ to understand significant differences between the wake development process and the mechanisms under different inflow velocities and wind speeds/directions. The model results suggested wind direction affects the range of the wake, with the wake extending longer when the wind and flow are parallel, whereas the wave is squeezed wider when the wind and flow are reversed. Interestingly, the temperature drop in the cold wake area shows differences with flow, which are different from the results observed by satellites. Another problem is that long-term satellite altimeter data indicates the likelihood of the Kuroshio main axis hitting Green Island is below 60%, meaning that the wake varies seasonally and partially disappears during the year. Therefore, this study also explore the effect of the Kuroshio main axis variation on the spatial scale of the Green Island wake, which involves seasonal wind-flow interaction.