Sea level variability along the Japanese coast in response to changes in the Kuroshio-Kuroshio Extension system

Abstract:

Sea level variability along the Japanese coast on interannual to decadal timescale was investigated using eddy-resolving ocean reanalysis data. An Empirical Orthogonal Function (EOF) analysis was performed to extract principal modes for the sea-level variability along the Japanese coast. The first mode that explains about 72% of the total sea-level variance exhibits a simultaneous sea-level change along the whole Japanese coast. In contrast, the second mode explaining about 11% of the total variance has a prominent dipole pattern along the south coast of Japan, whose bifurcation is located at the southern tip of the Kii Peninsula (between Kushimoto and Uragami). It was also shown that these two modes have a close relationship with changes in the Kuroshio-Kuroshio Extension (KE) system. Specifically, Kuroshio path fluctuations at the eastern flank of the Izu Ridge have a large impact on the EOF1 variability. Besides, former studies have pointed out that the latitudinal position of the Kuroshio around the Izu Ridge is closely related to the KE variability on interannual to decadal timescale. As a result, EOF1 is synchronized with the KE variability. In contrast, the EOF2 sea-level variability is sensitive to fluctuations of the Kuroshio path to the south of Kii Peninsula, implying that the EOF2 variability is understood as a response of the Kuroshio path variations south of Japan.