Characteristics of deep currents off Cape Shiono-misaki before and after formation of the large meander of the Kuroshio in 1981

[1] A long-lived (2-year) typical large meander (LM) path of the Kuroshio is reproduced in a high-resolution general circulation model (GCM) simulation with realistic topography, and the life cycle (formation, maintenance, and disappearance) of the LM is studied. The formation of the LM is triggered by a pair of upper layer anticyclonic and cyclonic eddies on the Kuroshio, with the cyclonic one on the downstream side. Upon reaching the western side of the Shikoku Basin south of Japan these anomalies induce a lower layer anticyclonic eddy. They enhance each other while they are carried eastward by the Kuroshio. Specifically, the southward flow on the eastern side of the lower anticyclonic eddy carries the upper cold cyclonic eddy offshore, resulting in the southward deflection of the Kuroshio path (large meander). These processes can be understood as a growth of baroclinic instability. A stationary LM is established when the westward tendency, caused by the beta effect owing to the large meridional displacement, counterbalances the eastward tendency, caused by the combination of advection and vortex induction owing to the curvature of the Kuroshio path. Large-scale disturbances from the upstream tend to strengthen the LM through baroclinic energy conversion. In contrast, small-scale disturbances from the upstream grow locally along the meandering Kuroshio front through baroclinic energy conversion. They extract cold waters from the cold cyclonic eddy of the LM as they flow away to the east. The horizontal extent of the cold cyclonic eddy is reduced, and the meander is carried eastward since the advection effect dominates over the beta effect that weakens as a result of the smaller meridional extent.

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“…[26] The same kind of transition is found in the dataassimilated fields in a study conducted by Usui et al Fukasawa and Teramoto [1986].…”

Section: Formationsupporting

confidence: 69%

“…They assimilated SSH from the satellite altimeter and in situ temperature and salinity in the interior into this model. Figure 8 depicts Fukasawa and Teramoto [1986].…”

Section: Formationmentioning

confidence: 99%

Dynamics of Kuroshio path variations in a high‐resolution general circulation model

Tsujino¹,

Usui²,

Nakano³

2006

J. Geophys. Res.

121

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“…Current meter moorings about 100 km to the north of Koshu Seamount showed the existence of eastward deep current temporarily enhanced during the transition from the NLM path to the LM path in 1981 [Fukasawa and Teramoto, 1986]. This agrees well with the model results of Endoh and Hibiya [2001] showing the enhancement of eastward deep current associated with the abyssal anticyclone over Koshu Seamount [see Endoh and Hibiya, 2001, Figure 11].…”

Section: Introductionsupporting

confidence: 76%

Interaction between the trigger meander of the Kuroshio and the abyssal anticyclone over Koshu Seamount as seen in the reanalysis data

Endoh¹,

Hibiya²

2009

Geophysical Research Letters

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The JCOPE (Japan Coastal Ocean Predictability Experiment) reanalysis data is analyzed to examine the transition from the non‐large meander path to the large meander path of the Kuroshio that occurred in 2004. It was preceded by the generation of “trigger meander” off the southeastern coast of Kyushu, which then propagated eastward. After passing Cape Shiono‐misaki, the trigger meander amplified rapidly over Koshu Seamount (located about 200 km to the south of Cape Shiono‐misaki) where the accompanying abyssal anticyclone was significantly enhanced. Strong downwelling occurred upstream of the meander trough where the abyssal anticyclone crossed the Kuroshio, causing the vertical vortex stretching (shrinking) in the upper (lower) ocean; the resulting enhanced abyssal anticyclone further amplified the meander trough in the upper ocean. All of these features agree well with the model results suggesting the importance of baroclinic instability over Koshu Seamount in the formation of the large meander path.

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“…In particular, Tsujino et al [2006] indicate that an anticyclonic eddy positioned at the upstream side of the trigger meander in the deep layer is important for the development. This idea is supported by Fukasawa and Teramoto [1986] who observed intensification of deep currents during the meander formation.…”

Section: Introductionmentioning

confidence: 54%

Application of singular vector analysis to the Kuroshio large meander

Fujii¹,

Tsujino²,

Usui³

et al. 2008

J. Geophys. Res.

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[1] Singular vector analysis is applied to the formation of the Kuroshio large meander south of Japan. We use a simulation run of an ocean general circulation model (OGCM), in which a large meander occurs, as the background state. Singular vectors are calculated by the Lanczos method in which the tangent linear and adjoint models of the OGCM are used. We apply an incremental correction approach for setting up the initial perturbation and averaging for the final norm in order to get modes reflecting nonlinear physics by filtering out high-frequency variations. The perturbation extracted as the leading right singular vector affects the formation of the large meander most if it is set to the background state two months before. When the perturbation is added, it enhances an anticyclonic eddy southeast of Kyushu in the upper layer, which induces downwelling north of it and develops an anticyclonic eddy in the deep layer. The anticyclonic eddy produces a cold anomaly at the downstream edge, and produces baroclinic instability there, resulting in further development of the large meander. In contrast, the anticyclonic eddy in the deep layer is weakened when the perturbation is subtracted, the development of the cold anomaly in the deep layer is delayed, and consequently the meander is not so well developed. Thus singular vector analysis reveals the role of the anticyclonic eddy approaching southeast of Kyushu in the upper layer, and indicates the importance of the anticyclonic eddy in the deep layer.Citation: Fujii, Y., H. Tsujino, N. Usui, H. Nakano, and M. Kamachi (2008), Application of singular vector analysis to the Kuroshio large meander,

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Characteristics of deep currents off Cape Shiono-misaki before and after formation of the large meander of the Kuroshio in 1981

Cited by 25 publications

References 5 publications

Dynamics of Kuroshio path variations in a high‐resolution general circulation model

Dynamics of Kuroshio path variations in a high‐resolution general circulation model

Interaction between the trigger meander of the Kuroshio and the abyssal anticyclone over Koshu Seamount as seen in the reanalysis data

Application of singular vector analysis to the Kuroshio large meander

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