The Kuroshio East of Taiwan: Moored Transport Observations from the WOCE PCM-1 Array

Abstract

Observations from the WOCE PCM-1 moored current meter array east of Taiwan for the period September 1994 to May 1996 are used to derive estimates of the Kuroshio transport at the entrance to the East China Sea. Three different methods of calculating the Kuroshio transport are employed and compared. These methods include 1) a ''direct'' method that uses conventional interpolation of the measured currents and extrapolation to the surface and bottom to estimate the current structure, 2) a ''dynamic height'' method in which moored temperature measurements from moorings on opposite sides of the channel are used to estimate dynamic height differences across the current and spatially averaged baroclinic transport profiles, and 3) an ''adjusted geostrophic'' method in which all moored temperature measurements within the array are used to estimate a relative geostrophic velocity field that is referenced and adjusted by the available direct current measurements. The first two methods are largely independent and are shown to produce very similar transport results. The latter two methods are particularly useful in situations where direct current measurements may have marginal resolution for accurate transport estimates. These methods should be generally applicable in other settings and illustrate the benefits of including a dynamic height measuring capability as a backup for conventional direct transport calculations. The mean transport of the Kuroshio over the 20-month duration of the experiment ranges from 20.7 to 22.1 Sv (1 Sv ϵ 10 6 m 3 s Ϫ1) for the three methods, or within 1.3 Sv of each other. The overall mean transport for the Kuroshio is estimated to be 21.5 Sv with an uncertainty of 2.5 Sv. All methods show a similar range of variability of Ϯ10 Sv with dominant timescales of several months. Fluctuations in the transport are shown to have a robust vertical structure, with over 90% of the transport variance explained by a single vertical mode. The moored transports are used to determine the relationship between Kuroshio transport and sea-level difference between Taiwan and the southern Ryukyu Islands, allowing for long-term monitoring of the Kuroshio inflow to the East China Sea.

Numerical study on the origins and the forcing mechanism of the phosphate in upwelling areas off the coast of Zhejiang province, China in summer

“…Furthermore, the model agrees quantitatively with observations. The model provides relatively good annual mean water fluxes 21.38 Sv (1.0 Sv = 1.0 × 10 6 m 3 /s) for ET, 1.03 Sv for TS, and 0.04 Sv for CR, which agree quantitatively with the measurements 21.45 Sv across ET (Johns et al, 2001), 1.20 Sv across TS (Isobe, 2008), and climatological mean 0.03 Sv for Changjiang River (Chu et al, 2009;Piao et al, 2010), respectively. As shown in Fig.…”

Large variability of the Kuroshio at 23.75°N east of Taiwan

“…Johns et al [2001] and Zhang et al [2001] suggested that the observed Kuroshio transport fluctuates with 100 day period rather than seasonal variation, which is presumably caused by the impinging of westward-propagating eddies into the Kuroshio. Further south at 21.5 N, Gilson and Roemmich [2002] calculated the Kuroshio geostrophic flow from the hydrographic data collected along the PX44_Ka transect (from Guam to southernmost Taiwan), and observed that the Kuroshio core current can shift from 121.3 E to 122.3 E at this transect.…”

Basinwide Integrated Volume Transports in an Eddy-Filled Ocean

“…It is assumed that an inverted barometer 80 correction has been applied to η, at a rate of ΔP A (t) = g ρ 0 Δη(t) (e.g., Fu and Pihos, 1994) so dynamically inactive changes Δη due to deviations in atmospheric pressure from the long-term mean ΔP A are removed. The geostrophic balance is a valid approximation even in the strongest (fastest) ocean current systems such as the Antarctic Circumpola r Current (Whitworth, 1983), the Gulf Stream (Sato and Rossby, 85 1995), the Kuroshio (Johns et al, 2001), the Agulhas Current (Beal and Bryden, 1999) or the Atlantic deep western boundary current .…”