Interannual to decadal variability of the Kuroshio Current in the East China Sea from 1955 to 2010 as indicated by in-situ hydrographic data

摘要

The temporal and spatial variability of the Kuroshio Current was analyzed. Current data were estimated from hydrographic data collected from areas within the central East China Sea (PN section) from 1955 to 2010 and the Tokara Strait (TK section) from 1987 to 2010. To reduce the bias caused by cruise-dependent spatial resolution among the data, grid-consistent temperature and salinity fields were reconstructed by use of a regression relationship to account for anomalies between observed stations and grid points. The mass imbalance problem between the PN and TK sections, which appears stochastically when viewed by use of the dynamic method, was solved by use of the inverse method. The estimated Kuroshio volume transport (KVT) was found to be closely consistent with that of current observations and had an uncertainty of 2.4?Sv. The KVT seemed to have neither a regime shift in approximately 1976 nor a sharply increasing trend. The KVT was dominated by 2–5?year modulating interannual variability with an amplitude of 2.8?Sv, followed by weak 20-year decadal variability with an amplitude of 0.33?Sv. Empirical orthogonal function analysis of the currents suggested that the temporal and spatial variability of the Kuroshio Current in the PN section was dominated by a transport mode, manifested by the high variability of current on the seaward side of current core with expansion or shrinkage of the core. In contrast, the temporal and spatial variability of the Kuroshio Current in the TK section was dominated by a meandering mode, as indicated by the migration of the Kuroshio axis in the south gap of the Tokara Strait.