Observations of an Extra-Large Subsurface Anticyclonic Eddy in the Northwestern Pacific Subtropical Gyre

Nan, Feng; Yu, Fei; Wei, Chuanjie; Ren, Qiang; Fan, Conghui

doi:10.4172/2155-9910.1000234

Cited by 22 publications

(35 citation statements)

References 45 publications

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“…High frequency of SSE is featured in several areas, including the latitudinal band between 9°N and 17°N, area east of the Ryukyu Islands, and Kuroshio extension region. In addition, observations have proven the existence of SSE within our study area (Chiang et al 2015;Nan et al 2017;Takikawa et al 2005;Zhang et al 2015;Zhang et al 2017). In the latitudinal band of 9°-17°N, the frequency of SSE is noticeably elevated, especially in the area to the east of The Philippines where it can reach 16%; however, the frequency of SE in this band is comparatively low (about 5%).…”

Section: Eddy Frequencysupporting

confidence: 58%

“…Most of the observed SSEs were found nonlinear, which means that SSE can have considerable impact in the movement of heat and mass transport within the subsurface layer, especially in some regions with abundant SSE. The dynamical mechanism of SSE is complex, and it is often related to the regional background circulation, water mass characteristics, and/or topographic boundaries (Hormazabal et al 2013;Nan et al 2017;Takikawa et al 2005).…”

Section: Discussionmentioning

confidence: 99%

“…Generally, SSEs are triggered by instability of the undercurrent or subduction of mode water (Oka et al 2009;Takikawa et al 2005). Previous studies have proven that SSE can strongly influence intermediate or deeper ocean layers by affecting the subsurface circulation, pathways of water masses, and redistribution of heat, salt, and momentum (Andrade et al 2014;Colas et al 2012;Nan et al 2017;Pelland et al 2013). Unlike surface eddies (SEs), which can be characterized using satellite altimeter data, SSEs have weak surface expression, and they are poorly understood because of the lack of their systematic measurement (Chaigneau et al 2011;Gordon et al 2017;Johnson and McTaggart 2010).…”

Section: Introductionmentioning

confidence: 99%

“…In December 2013, a subsurface lens of water from the Andaman Sea was captured in the Bay of Bengal (Gordon et al 2017). Nan et al (2017) detected an extra-large subsurface anticyclonic eddy with horizontal scale of 470 km in the Northwest Pacific subtropical gyre. Their analysis indicated that the SSE formed in the region of Subtropical Mode Water and, then, propagated westward for over 1500 km.…”

Section: Introductionmentioning

confidence: 99%

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Study of subsurface eddy properties in northwestern Pacific Ocean based on an eddy-resolving OGCM

Nan

2019

Ocean Dynamics

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A method based on the Okubo-Weiss parameter was used to detect subsurface eddies (SSEs) with an eddy-resolving ocean general circulation model. Statistical analyses showed that SSEs are ubiquitous in the northwestern Pacific Ocean. Three regions were found to have high probability of SSE, which are as follows: the latitudinal band between 9°N and 17°N, the Kuroshio extension region, and the area east of the Ryukyu Islands. Although surface eddies (SEs) were found distributed widely within the zonal band of the Subtropical Counter Current, few SSEs were found there. In contrast, few SEs were found to the east of The Philippines, whereas SSEs were abundant. The kinetic energy contained within SSE was found comparable in magnitude with that of SE. During 1993, about 2569 and 2099 SSEs (at a depth of about 400 m) were observed to be anticyclonic and cyclonic, respectively; thus, SSEs tended to be anticyclonic. The mean radius, lifespan, and propagation speed of SSE in this study were about 60 km, 50 days, and 6.6 cm/s, respectively. The propagation speed showed a wave-like decrease with increasing latitude. Some long-lived SSEs were found to persist for longer than 4 months and to move thousands of kilometers. About 89% of SSEs were nonlinear for at least half their lifespan, which implies that SSE can trap interior fluid during translation. Trajectories revealed that SSEs propagate nearly due west with only small meridional deflection. The findings of this study will contribute to the enrichment of our knowledge regarding SSE in the northwestern Pacific Ocean.

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Section: Eddy Frequencysupporting

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Study of subsurface eddy properties in northwestern Pacific Ocean based on an eddy-resolving OGCM

Nan

2019

Ocean Dynamics

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“…The lens structure of isopycnals is typical for subsurface eddies, and the existence of the low-potential vorticity (PV) inside the eddy center was thought to be the major reason for this structure. Relative vorticity is usually much smaller than planetary vorticity in most of the interior of the ocean, if ignoring the effects of the relative vorticity; the PV has the following expression (Pedlosky, 1996;Stewart, 2008;Nan et al, 2017):…”

Section: Physical Propertiesmentioning

confidence: 99%

The Physical-Biogeochemical Responses to a Subsurface Anticyclonic Eddy in the Northwest Pacific

Ding

Ren

et al. 2022

Front. Mar. Sci.

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Due to the unique physical processes of mesoscale eddies, the physical and biogeochemical properties within the subsurface anticyclonic eddy (SSAE) and in the surrounding water are distinct. Analyses using satellite and model data have revealed distinct seasonal variations in the central potential density structure of a long-standing SSAE south of Japan; this SSAE exhibits a normal concave isopycnals structure from January to April and a convex lens isopycnals structure from May to December, and these variations may be related to the subduction of low-potential vorticity (PV) mode water. In contrast to the idea of the self-sustained oscillation mechanism, the strength of the SSAE was enhanced due to the eddy kinetic energy provided by dramatic increasing of the positive baroclinic conversion rate during the Kuroshio path transition period from the non-large meander (NLM) path to the large meander (LM) path. Twofold to threefold enhancement of chlorophyll (CHL) was detected in the subsurface CHL maximum layers at the core of the SSAE, and this enhancement was related to the injection of nutrients into the euphotic layer due to winter mixing and the convex of isopycnals. During the period from May to December, elevated CHL and dissolved oxygen (DO) levels and reduced nitrate levels were observed along the periphery of the eddy below the maximum subsurface CHL anomaly depth. The combined result of these two processes: (1) the central downward displaced isopycnals caused by intensified SSAE, and (2) winter mixing deepened to the nutricline due to the thickened mixed layer depth (MLD) and weakened stratification in winter 2017 (during the NLM period) may have led to numerous nutrients and CHL enrichments throughout the mixed layer, thus generating a CHL bloom in the following April. The SSAE intensified in winter 2018 (during the LM period), whereas the shallower MLD and stronger stratification limited the depth of CHL downward displacement.

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Interannual modulation of subthermocline eddy kinetic energy east of the Philippines

Hui

Zhang

Wang

et al. 2022

Preprint

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Interannual variation of subthermocline eddy kinetic energy (EKE) east of the Philippines is investigated based on mooring measurements during 2015-2019 and ocean state estimates during 1995-2017 from the Oceanic General Circulation Model for the Earth Simulator (OFES). Prominent interannual variation of EKE is detected below the thermocline east of the Philippine coast, which is closely related to the El Niño and Southern Oscillation (ENSO) events and generally lags the Nino3.4 index by 14 months. Further energy diagnostic analysis indicates that the interannual variation of subthermocline EKE is controlled by both baroclinic and barotropic instability of the background flows and dominated by the barotropic instability especially. Barotropic instability in the southern part of the Philippine coast is associated with the subsurface component of the quasi-permanent anticyclonic eddy Halmahera Eddy (HE), while that in the northern part is closely related to the Mindanao Undercurrent (MUC). Both HE and MUC are modulated by the ENSO events. When El Niño occurs, negative sea surface height anomalies appear near the dateline and propagate westward in the form of the first mode baroclinic Rossby wave, exerting delayed impacts upon the western boundary currents east of the Philippine coast and further modulating the interannual variation of subthermocline EKE. Moreover, the barotropic energy conversion rate and its corresponding subthermocline EKE at lower latitudes responds relatively faster to ENSO due to the higher Rossby wave phase speed there.

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Observations of an Extra-Large Subsurface Anticyclonic Eddy in the Northwestern Pacific Subtropical Gyre

Cited by 22 publications

References 45 publications

Study of subsurface eddy properties in northwestern Pacific Ocean based on an eddy-resolving OGCM

Study of subsurface eddy properties in northwestern Pacific Ocean based on an eddy-resolving OGCM

The Physical-Biogeochemical Responses to a Subsurface Anticyclonic Eddy in the Northwest Pacific

Interannual modulation of subthermocline eddy kinetic energy east of the Philippines

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