Evolution of the Kuroshio Tropical Water from the Luzon Strait to the east of Taiwan

Abstract

This study examines the evolution of the Kuroshio Tropical Water (KTW) from the Luzon Strait to the I-Lan Ridge northeast of Taiwan. Historical conductivity temperature depth (CTD) profiles are analyzed using a method based on the calculation of the root mean square (rms) difference of the salinity along isopycnals. In combination with analysis of the distribution of the salinity maximum, this method enables water masses in the Kuroshio and the vicinity, to be tracked and distinguished as well as the detection of the areas where water masses are modified. Vertical and horizontal eddy diffusivities are then calculated from hydrographic and current velocity data to elucidate the dynamics underlying the KTW interactions with the surrounding water masses. Changes in KTW properties mainly occur in the southern half of the Luzon Strait, while moderate variations are observed east of Taiwan on the right flank of the Kuroshio. In spite of a front dividing the KTW from the South China Sea Tropical Water (SCSTW) on Kuroshio׳s western side, mixing between these two water masses seemingly occurs in the Luzon Strait. These water masses׳ interaction is not evident east of Taiwan. The estimation of eddy diffusivities yields high horizontal diffusivities (Kh~102m2s−1) all along the Kuroshio path, due to the high current shear along the Kuroshio׳s flanks. The vertical diffusivity approaches 10−3m2s−1, with the highest values in the southern Luzon Strait. Instabilities generated when the Kuroshio encounters the rough topography of this region may enhance both vertical and horizontal diffusivities there.