Observations of flow variability through the Kerama Gap between the East China Sea and the Northwestern Pacific

Na, Hanna; Wimbush, Mark; Park, Jae Hun; Nakamura, Hirohiko; Nishina, Ayako

doi:10.1002/2013jc008899

Cited by 27 publications

(32 citation statements)

References 25 publications

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“…Rather, the observations suggest that indirect eddy effects drive the transport variability at the PN Line, possibly via eddyinduced "streamers" that flow around the islands due to conservation of circulation (Andres and Cenedese, 2013 in the eddy (cyclonic or anti cyclonic), these streamers add to or subtract from the net Kuroshio transport at the PN Line. This idea of eddy-induced flow through the island chain is also consistent with strong flow variability observed in the Kerama Gap in data from an array of CPIESs and current meter moorings (Na et al, 2014) that show transport variability through the gap correlates with the presence of cyclones and anticyclones in the Philippine Basin adjacent to the islands just southwest of the Kerama Gap. In contrast to the western Philippine Basin, transport variability observed at the PN Line (with CPIESs) is well correlated with transport variability in the Kuroshio where it exits the East China Sea through Tokara Strait (from eight hydrographic sections; Nakamura et al ) is consistent with the speeds of the velocity cores in the mean cross section here (Figure 3c).…”

supporting

confidence: 80%

Mean Structure and Variability of the Kuroshio from Northeastern Taiwan to Southwestern Japan

Andres¹,

Jan²,

Sanford³

et al. 2015

Oceanog

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Mean Structure and Variability of the Kuroshio from Northeastern Taiwan to Southwestern JapanABSTRACT. In the subtropical western North Pacific Ocean, the Kuroshio delivers heat, salt, and momentum poleward, much like its North Atlantic analog, the Gulf Stream. Though the Kuroshio generally flows along the western boundary from Taiwan to southeastern Japan as an "attached" current, the Kuroshio's strength, vertical structure, and horizontal position undergo significant temporal and spatial variability along this entire route. Ubiquitous mesoscale eddies and complicated topography associated with a string of marginal seas combine to make the western North Pacific a region with complex circulation. Here, we synthesize results from the recent US Origins of the Kuroshio and Mindanao Currents and Taiwan Observations of Kuroshio Transport Variability observational programs with previous findings to build a comprehensive picture of the Kuroshio on its route from northeastern Taiwan to southeastern Japan, where the current finally transitions from a western boundary current into the Kuroshio Extension, a vigorously meandering free jet. in the western North Pacific over the past decades, many of them supported by ONR, that have focused on different sections along the Kuroshio (Table 1). Here, we summarize some of these earlier field programs and synthesize them with OKMC/OKTV results to describe the downstream evolution of the Kuroshio along its route from the western Philippine Basin through the East China Sea to south of Japan (Figure 1a). MEASURING THE KUROSHIODue to the rich eddy field in the western North Pacific (Figure 2a), individual synoptic sections across the Kuroshio from shipboard measurements are often not representative of the current's mean state. Longer duration measurements (or many crossings) are needed to estimate the current's mean transport and velocity structure. Since 1991, arrays of inverted echo sounders (IESs) have been deployed at various sections across the Kuroshio (e.g., Table 1 and the green lines in Figure 3a) to measure variability at hourly resolution for durations of one year or more. In most cases, the IESs were also equipped with pressure sensors (PIESs) and additional current sensors (CPIESs) or horizontal electric field sensors (HPIESs) to help establish the Kuroshio's time-varying position, absolute geostrophic transport, and velocity structure (see Meinen et al., 2002;Donohue et al., 2010;and Szuts, 2012, for reviews of the methodologies and the title page photo [opposite] for an image of a PIES). One of these experiments was along the Affiliated Surveys of the Kuroshio off Cape Ashizuri (ASUKA) Line, which extends 1,000 km southeastward from Shikoku, Japan, into the Philippine Basin (Figure 3a). A full array of instruments was deployed there from 1993 to 1995 (Book et al., 2002) with a reduced two-IES array maintained through (Kakinoki et al., 2008. Two IES arrays were also deployed along the PN Line, a repeat hydrographic line in the East China Sea northwest of Okinawa (labele...

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supporting

confidence: 80%

Mean Structure and Variability of the Kuroshio from Northeastern Taiwan to Southwestern Japan

Andres¹,

Jan²,

Sanford³

et al. 2015

Oceanog

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“…Through strait northeast of Taiwan and the Kerama gap, they influence the spatio-temporal structure of the Kuroshio in the ECS (Zhang et al, 2001;Na et al, 2014). With this effect, the Kuroshio volume transport (KVT) may exhibit significant intraseasonal variability as demonstrated by Andres et al (2008) using continuous 13-month in-situ observation at the PN Section ( Fig.…”

Section: Introductionmentioning

confidence: 99%

Seasonal variability of the Kuroshio Current at the PN Section in the East China Sea based on in-situ observation from 1987 to 2010

Wei

Pei

2015

Acta Oceanol. Sin.

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As the spatio-temporal variability of the Kuroshio is highly influenced by mesoscale eddies, representing its seasonal variability characteristics requires sufficiently long term observations to reduce the uncertainties. Geostrophic velocity data estimated from hydrographic observation from 1987 to 2010 and the shipboard ADCP velocity data from 1993 to 2008 at the PN Section in the central East China Sea are collected to view the seasonal variability objectively. From both types of observation, it is found that the seasonal climatology mean of the Kuroshio Current exhibits significant difference in three areas, which are located at the Kuroshio Current core and its two flanks in a shallow layer less than 300 m, with the weakest northeast current at the core in autumn, the strongest counter current on the right flank in spring, and the strongest northeast current on the left flank in autumn, respectively. The seasonal variance of the Kuroshio Current also exhibits significant difference on the offshore side of the Kuroshio, with larger variance in spring and summer while smaller variance in autumn and winter. For the current parallel to the PN Section, the ratio of the seasonal variability component to the intraseasonal variability component is relatively smaller than that for the current perpendicular to the PN Section. Further analyses indicate that the seasonal variability at the PN Section is tightly linked to the upstream and downstream current variability.

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“…[] and Na et al . [] revealed that the temporal variability of transport through the Kerama Gap, located just south of these four channels, is related to the arrival of mesoscale eddies propagating from the east. In their studies, the mesoscale eddy is assumed to be surface intensified.…”

Section: Residual Currentsmentioning

confidence: 99%

“…The Kerama Gap south of Okinawa is the most well‐known and deepest channel, with a sill depth of 1050 m, and connects the ECS with the surrounding ocean. Previous studies have investigated the impact of water exchanges via the Kerama Gap on the interaction between the Kuroshio and the Ryukyu Current [ Nitani , ; Morinaga et al ., ; Andres et al ., ; Nakamura et al ., ; Na et al ., ; Yu et al ., ; Nishina et al ., ]. Andres et al .…”

Section: Introductionmentioning

confidence: 98%

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Tidal and residual currents across the northern Ryukyu Island chain observed by ferryboat ADCP

et al. 2017

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Ferryboat Acoustic Doppler Current Profiler (ADCP) data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern Ryukyu Island chain (RIC) between the islands of Okinawa and Amamioshima. In this region, the M2 tide current is the strongest tidal component, and the K1 tide current is the strongest diurnal tidal component. The corresponding maximum amplitudes are 40 and 34 cm s−1, respectively. After removal of the tidal currents, the mean volume transport, 1.5 ± 2.7 Sv, flows into the East China Sea (ECS) from the western North Pacific through four channels in this area. In an empirical orthogonal function (EOF) analysis performed to clarify the temporal and spatial variability of currents through the four channels, the first two EOF modes account for 71% and 18% of the total variance, respectively. The EOF1 mode shows a clear bottom‐intensified mode through the deep channel, which is likely to be formed by the propagation of bottom‐trapped long topographic Rossby wave caused by the impingement of westward‐propagating mesoscale eddies upon the eastern slope of the northern RIC. The EOF2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the Kuroshio flow region around the northern RIC in October–November. This study provides observational evidence of the water exchanges across the northern RIC, which is essential for constructing a circulation scheme in the North Pacific subtropical western boundary region.

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Observations of flow variability through the Kerama Gap between the East China Sea and the Northwestern Pacific

Cited by 27 publications

References 25 publications

Mean Structure and Variability of the Kuroshio from Northeastern Taiwan to Southwestern Japan

Mean Structure and Variability of the Kuroshio from Northeastern Taiwan to Southwestern Japan

Seasonal variability of the Kuroshio Current at the PN Section in the East China Sea based on in-situ observation from 1987 to 2010

Tidal and residual currents across the northern Ryukyu Island chain observed by ferryboat ADCP

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