Weakest winter <scp>S</scp>outh <scp>C</scp>hina <scp>S</scp>ea western boundary current caused by the 2015–2016 <scp>E</scp>l <scp>N</scp>iño event

Zhao, Ruixiang; Zhu, Xiao‐Hua

doi:10.1002/2016jc012252

Cited by 26 publications

(24 citation statements)

References 26 publications

(38 reference statements)

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“…We then applied a 10-day running average, obtaining a time series SSHD sat-sat . The correlation (r = 0.70, which exceeds the 99% confidence level) between the observations and SSHD sat-sat was not as strong as the near 0.90 values found in previous studies in other regions such as the Kuroshio 9,16 , the RC near Okinawa 30 , and the South China Sea 31,32 , because high-frequency processes were strong near RES1 (which was also seen in CPIES bottom pressure records) and may contaminate the altimeter data through aliasing. Therefore, we used the sea-level difference between RES4 and Ishigakijima instead (see Fig.…”

Section: Discussioncontrasting

confidence: 63%

Tempo-spatial variations of the Ryukyu Current southeast of Miyakojima Island determined from mooring observations

Zhao

Nakamura

Zhu

et al. 2020

Sci Rep

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The origin, structure, and variability of the Ryukyu Current (RC) have long been debated, mostly due to limited observations. A mooring array, deployed for two years southeast of Miyakojima in the southern portion of the Ryukyu Island chain, has provided, for the first time, data confirming the existence and revealing the characteristics of the RC in that upstream region, including its velocity structure and variability. The observations show a shoreward-intensified current flowing northeastward, with a subsurface core located near the 1,000 m isobath and having a record-long mean speed of up to 19.4 cm s −1 at 500 m depth. Estimated volume transport across the observation section had mean 9.0 Sv (1 Sv = 10 6 m 3 s −1) and standard deviation 8.7 Sv. The RC shows significant barotropic character compared with other similar mid-latitude currents. The Kuroshio is the strongest western boundary current in the Pacific Ocean. Consequently it has long been the focus of many scientific studies 1,2. After it enters the East China Sea (ECS), the Kuroshio flows northeastward, west of the Ryukyu Island chain, until it reaches the region south of Kyushu, Japan and exits through the Tokara Strait (Fig. 1a). However, studies 3,4 have also indicated the existence of another strong portion of the western boundary current, namely the Ryukyu Current (RC) flowing northeastward just east of the Ryukyu Island chain, accounting for the large difference in volume transport of the Kuroshio between the ECS (19 − 28 Sv; 1 Sv = 10 6 m 3 s −1) 5-7 and the sea off southern Japan (42~65 Sv) 8,9. Compared to the Kuroshio west of the Ryukyu Island chain, which is surface intensified and relatively stable, the RC features a strong subsurface velocity core 10,11 and large spatio-temporal variability caused by mesoscale eddies propagating from the Pacific 12,13. Previous studies have also suggested the RC's variability may be related to that of the Kuroshio East of Taiwan 14-16. Interactions between the RC and the Kuroshio via the Kerama Gap (Fig. 1b) contribute to the variability of the Kuroshio in the ECS and play a key role in water mass exchange between the ECS and the North Pacific 17-20. The RC carries a large mass of water, heat, and nutrients poleward 21,22 , greatly enhancing the Kuroshio when the two currents merge east of the Tokara Strait. Although the RC is important to the circulation of the North Pacific, its mean structure and spatio-temporal variability remain unclear, due to limited observations. Snapshots of hydrographic casts 23,24 can be greatly affected by mesoscale eddies; therefore, long-term mooring deployments are needed to remove aliases. Previous mooring observations have revealed the velocity structure and variability of the RC southeast of Amami-Oshima 3 and Okinawa 21,25 , which are in the downstream region of the RC. In the upstream region, two moored current meters showed a persistent northeastward current southeast of Miyakojima 26 but were not able to determine the structure of the RC there.

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Section: Discussioncontrasting

confidence: 63%

Tempo-spatial variations of the Ryukyu Current southeast of Miyakojima Island determined from mooring observations

Zhao

Nakamura

Zhu

et al. 2020

Sci Rep

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“…Therefore, stronger upwelling was observed in the NSCS during the summer of 2016 than during the summer of 2008, although the local wind of 2008 was more favorable to upwelling. Previous studies showed that the variability in the basin‐scale current in the NSCS is closely related to the variability in the basin‐scale wind, Luzon intrusion, and eddy activities (Shu et al, , ; Zhao & Zhu, ; Zhao et al, ; Zhu et al, ). Figure c shows that the difference in basin‐scale wind between 2008 and 2016 was southwestward in the NSCS basin, which could not drive the strong northeastward current in the shelf in the summer of 2016 compared with that in 2008.…”

Section: Discussionmentioning

confidence: 99%

The Contribution of Local Wind and Ocean Circulation to the Interannual Variability in Coastal Upwelling Intensity in the Northern South China Sea

Shu

Wang

Feng³

et al. 2018

JGR Oceans

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Using in situ data, satellite observations, and model outputs, we analyzed the interannual variability in coastal upwelling intensity in the northern South China Sea. Comparing coastal upwelling observed from three cruises during the summers of 2008 and 2016, we found that coastal upwelling was stronger during 2016 compared to 2008, although the local upwelling favorable wind was stronger in 2008. The stronger near-bottom cross-shelf current and shallower thermocline in the slope resulted in stronger upwelling intensity during the summer of 2016. The topographic position index (TPI), which is defined by the sea surface temperature difference between one center cell and its neighbors, was used to quantify the interannual variability in upwelling. Stronger (weaker) upwelling intensity occurred during the summers of ) when the local wind was more favorable (less favorable) to coastal upwelling. The correlation coefficient between the area-weighted TPI and alongshore wind speed was À0.60, thereby confirming that local wind is the primary dynamical factor controlling the interannual variability in upwelling intensity. The correlation coefficient between the area-weighted TPI and the eastward boundary current transport averaged between the 75-and 100-m isobaths on the shelf was À0.42, indicating that the interannual variability in large-scale circulation in the northern South China Sea also contributes to the interannual variability in upwelling intensity. The anomalously shallow thermocline in the summer of 2016 was likely associated with the strong 2015-2016 El Niño event through planetary wave propagations.Plain Language Summary Coastal upwelling, transporting deep, cold, saline, and nutrient-rich water to the surface result in high levels of primary production and fishery production. The coast of the northern South China Sea (NSCS) features seasonal coastal upwelling during the boreal summer. The summer southwesterly wind is widely regarded as the main driving mechanism for coastal upwelling in the NSCS. Previous studies have shown that the interannual variability in coastal upwelling intensity is largely controlled by the interannual variability in local winds in the NSCS, which is closely related to the El Niño-Southern Oscillation. Based on in situ data, we found that the upwelling was much stronger during 2016 than during 2008, though the local wind was more favorable to upwelling during 2008, which indicated that local wind is not the sole factor controlling the interannual variability in upwelling intensity in the NSCS. Further studies showed that, beside the locale wind, the interannual variability in shelf circulation could also contribute to the interannual variability in coastal upwelling intensity due to the topographically induced upwelling (induced by the interaction between northeastward large-scale current and alongshore variable topography) in the NSCS. In addition, thermocline depth variation on interannual time scale likely influences the coastal upwelling intensity in the NSCS.

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“…LS transport advects the North Pacific signal into the SCS and then impacts the dynamic state of the SCS (Nan et al, 2015;Qu et al, 2000Qu et al, , 2005Qu et al, , 2006Qu et al, , 2009Zhang et al, 2015). LS transport, as a major component of the SCS throughflow (Qu et al, 2004(Qu et al, , 2005Wang et al, 2006), also modulates the thermodynamic state of the SCS (Xiao et al, 2018;Zeng et al, 2014Zeng et al, , 2016Zhao & Zhu, 2016) and plays an important role in the interannual variability of the Indonesian throughflow (Fang et al, 2003;Qu et al, 2009;.…”

Section: Introductionmentioning

confidence: 99%

“…The largescale Kuroshio intrusion, which carries saline and warm water into the SCS, induces a high-pressure belt along the northern SCS slope and material exchange between the continental shelf and open sea . In the northern SCS, there is a southwestward (northeastward) slope current in winter (summer), which is the northern part of the SCS west boundary current (Shu et al, 2018;Zhao & Zhu, 2016;Zhu et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

The Linkage of Kuroshio Intrusion and Mesoscale Eddy Variability in the Northern South China Sea: Subsurface Speed Maximum

Wang

Zeng

Chen

et al. 2020

Geophysical Research Letters

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In situ data suggest that there is a subsurface speed maximum between 70 and 120 m in the Kuroshio, which is first revealed by the directly velocity observation. The subsurface speed maximum can also be advected into the largest marginal sea in the tropics, that is, the South China Sea (SCS). As it enters the SCS, its depth shoals to between 40 and 70 m and then finally disappears in the western northern SCS. Strong subsurface speed maximum intrusion results in strong baroclinic instability, which triggers vigorous baroclinic conversion, consequently the active mesoscale eddy variability in the northern SCS, and vice versa. Our study highlights this intuitive bridge connecting the Kuroshio intrusion and the mesoscale eddy activities in the northern SCS.

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Weakest winter South China Sea western boundary current caused by the 2015–2016 El Niño event

Cited by 26 publications

References 26 publications

Tempo-spatial variations of the Ryukyu Current southeast of Miyakojima Island determined from mooring observations

Tempo-spatial variations of the Ryukyu Current southeast of Miyakojima Island determined from mooring observations

The Contribution of Local Wind and Ocean Circulation to the Interannual Variability in Coastal Upwelling Intensity in the Northern South China Sea

The Linkage of Kuroshio Intrusion and Mesoscale Eddy Variability in the Northern South China Sea: Subsurface Speed Maximum

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