April 28: "Observations of the Kuroshio in the East China Sea: local, regional, and basin-wide perspectives on a western boundary current"
The Kuroshio is the western boundary current of the North Pacific mid-latitude gyre. An observational study of the Kuroshio was conducted using data collected in the East China Sea (ECS) north of Okinawa from December 2002 through November 2004 with an array of inverted echo sounders and acoustic Doppler current profilers. Using these data, Kuroshio velocity structure and transport time series were obtained. Net absolute transport ranges between 4 and 29 Sv and has spectral peaks at periods of 60, 15 and 11 days. The mean net absolute transport is 18.5 ± 0.8 Sv. In conjunction with these in situ measurements, satellite altimeter data were used to extend the Kuroshio transport time series back to 1993. Comparison with net Ryukyu Current transport southeast of Okinawa shows that their mean sum (24 Sv), is less than the mean predicted Sverdrup transport. Additionally, Kuroshio and Ryukyu Current transports are positively correlated, with 60 day lag, due to the effect of mesoscale eddies impinging on the Kerama Gap. Finally, annually-averaged Kuroshio and Ryukyu Current transports correlate positively with the Pacific Decadal Oscillation (PDO) index. The correlations, r, which are highest at zero lag, are 0.76 for the Kuroshio and 0.49 for the Ryukyu Current. The combined transport variation correlated with PDO index variation is about 4 Sv. PDO index is strongly negatively correlated with NCEP wind stress curl over the central North Pacific at 20°–30°N.