The Wintertime Subtropical Current in the Northwestern Pacific

The strong wintertime westward current in the northwestern Pacific between 18°N and 23°N was investigated using data from satellite-tracked drifters. The decadal strengthening of the negative wind stress curl and trade wind in the subtropical area north of Hawaii and west of 150°E drives the decadal variability of this wintertime current. The Sverdrup transport computed from a high-resolution (1° × 1°) wind stress reanalysis product reproduces the Wintertime Subtropical Current (WSTC) well, and shows that its Sverdrup transport increases in excess of 15 Sv (1 Sv = 106 m3 s–1) from the early 1970s to the 1990s. The annual variation of the WSTC transport is well correlated with the North Pacific Index, which represents the strength of the Aleutian Low before the 1988/89 climate shift, but the correlation with teleconnection patterns or climate indices becomes weak after the 1988/89 shift. The annual fluctuations of WSTC transport are found to be reflected in the springtime Kuroshio transport south of Japan.