The Kuroshio Current System as a jet and twin “relative” recirculation gyres embedded in the Sverdrup circulation

Nakano, Hideyuki; Tsujino, Hiroyuki; Furue, Ryo

doi:10.1016/j.dynatmoce.2007.09.002

Cited by 48 publications

(37 citation statements)

References 48 publications

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“…Among the three models, the Kuroshio recirculation gyre, recognized as the westward tilt of the surface height contours, was better simulated by the eddy-resolving model (NPERM5). Because the separation latitude of the Kuroshio and the strength of the recirculation gyre strongly depend on the magnitude of vorticity advection [Nakano et al, 2008], this improvement may result from the increased nonlinear effect in the eddy-resolving model. The better simulation of the Kuroshio recirculation gyre suggests that the distributions of the mode waters may also be simulated better by the NPERM5 model.…”

Section: Model and Experimentsmentioning

confidence: 99%

Decadal variability of the Subtropical Front of the western North Pacific in an eddy‐resolving ocean general circulation model

Yamanaka¹,

Ishizaki²,

Hirabara³

et al. 2008

J. Geophys. Res.

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[1] We examined decadal variability of the Subtropical Front (STF) of the western North Pacific by using a North Pacific ocean general circulation model (OGCM), comparing the results of three simulations with different horizontal resolutions. In the long-term mean fields, the eddy-resolving model (10 km) was able to simulate the distributions of the STF and the associated Subtropical Countercurrent (STCC) between 20°N and 30°N better than either the non-eddy-resolving model (100 km) or the eddy-permitting model (20 km) because it simulated the Kuroshio recirculation gyre more realistically. The simulated STF intensity exhibited significant decadal-scale variations: it was stronger in the late 1970s and weaker in the early 1990s. During these two periods, the simulated mode waters showed corresponding differences in their potential vorticity minima density and paths. We also investigated the relationship between the decadal-scale STF variability and atmospheric forcing. The results suggest that the decadal-scale STF variability can be largely explained by changes in the mode waters formed in the western North Pacific and advected to north of the STF by the subtropical gyre in response to a change in surface westerly winds that occurred in the mid-1970s.

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Section: Model and Experimentsmentioning

confidence: 99%

Decadal variability of the Subtropical Front of the western North Pacific in an eddy‐resolving ocean general circulation model

Yamanaka¹,

Ishizaki²,

Hirabara³

et al. 2008

J. Geophys. Res.

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“…1, the jet is located along the front of low potential vorticity water advected by the inertial boundary current and high potential vorticity water generated by the viscous boundary layer as in Kiss (2002). Northern and southern recirculation gyres in the flank of the jet, mentioned in Nakano et al (2008), can also be seen in both the upper and lower layers, which imply that these recirculations create strong barotropic structure. The velocity of the extended jet is rapidly damped for x .…”

Section: A Two Typical Solutionsmentioning

confidence: 95%

“…In addition, Nakano et al (2008) showed that the latitude of the extension jet does not depend on the shape of the western boundary. These results lead us to expect that the factor that determines the latitude of the extension jet is the distribution of external forcing.…”

Section: Dependence On Meridional Distribution Of Ekman Pumping Vementioning

confidence: 99%

“…Although the width of the viscous boundary layer in the real ocean is unknown, we may assume that it is less than the inertial boundary layer width. In the numerical experiment of Nakano et al (2008), d M was approximately 0.4, but they used biharmonic viscosity. In the present paper, d M 5 0:3 was used as the reference value that corresponded to n 5 50 (m 2 s…”

Section: Modelmentioning

confidence: 99%

“…Because the separation latitude of the Kuroshio coincides with that of the southern coast of Japan and the Gulf Stream separates north of Cape Hatteras, the effects of topographic features of the coastal boundary and/or bottom have also been studied (see, e.g., Dengo 1993;Özgökmen et al 1997;Marshall and Tansley 2001). Recently, Nakano et al (2008) showed, by using an eddyresolving ocean GCM with no-slip boundary condition, that the model Kuroshio separates around the same latitude and a realistic Kuroshio Extension accompanying the recirculation gyres occurs even when the topography including the Japan Islands is removed. Therefore, the separation of western boundary currents and their eastward extensions can occur even in a rectangular basin (bounded by meridional and zonal coastlines), although the topography must affect the current in real oceans.…”

Section: Introductionmentioning

confidence: 99%

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Latitude of Eastward Jet Prematurely Separated from the Western Boundary in a Two-Layer Quasigeostrophic Model

Sue

Kubokawa

2015

Journal of Physical Oceanography

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This paper investigates the formation of eastward jets extended from western boundary currents, using a simple two-layer quasigeostrophic (QG) model forced by a wind stress curl consistent with the formation of a subtropical gyre. The study investigated the dependency of the latitude of the eastward jet on various parameters and on the meridional distribution of the Ekman pumping velocity. The parameters considered in the present study included the viscous and inertial western boundary layer width, the parameter representing the degree of the partial-slip boundary condition, the ratio of the upper-to lower-layer depth, and the bottom friction. With the parameters used, two types of stable structures are found in the time-mean field. One type of structure represented the ''prematurely separated jet case,'' in which the eastward extension jet was located far south of the northern boundary of the subtropical gyre, as is the Kuroshio Extension; the other type was the ''gyre boundary jet case,'' in which the eastward jet occurred along the northern boundary. The initial condition decides which type of structure would occur. When the prematurely separated jet case occurred, the authors found that the latitude of the eastward jet depended very little on the parameters. In addition, this study also observed that the latitude was determined by the meridional distribution of the Ekman pumping velocity. The eastward extension jet was usually located near the latitude that was half of the maximum value of the Sverdrup streamfunction and satisfied an integral condition derived from the QG potential vorticity equation.

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Argo data assimilation and its effect on climate state estimation and forecasting in the western North Pacific using a coupled model

et al. 2015

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In this study, we investigated the effects of ocean subsurface data (Argo data) on climate state estimation and forecasting, focusing on the reproduction of North Pacific subtropical mode water (STMW) using a four-dimensional variational data assimilation system with a coupled model. We produced two reanalysis plus forecast data sets for the ocean and atmosphere in 2010 using a 3 month assimilation period: the first including Argo data (Argo case) and the second did not include Argo data (control case). In the control case, the Kuroshio, Kuroshio Extension front, and recirculation gyres along the front were not adequately reproduced. Consequently, there were large biases in temperature and salinity in the western North Pacific. The assimilation of Argo data effectively corrected these biases and significantly improved reproduction of the Kuroshio fronts and recirculation gyres, resulting in a more realistic reproduction of the winter mixed layer and STMW. The correction of these biases is critical to the 1-3 year predictions of the STMW core properties, and the assimilation of Argo data enables prediction of these properties for more than a year. We showed that assimilation of Argo data affects the surface atmospheric temperature above the STMW formation region.

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The Kuroshio Current System as a jet and twin “relative” recirculation gyres embedded in the Sverdrup circulation

Cited by 48 publications

References 48 publications

Decadal variability of the Subtropical Front of the western North Pacific in an eddy‐resolving ocean general circulation model

Decadal variability of the Subtropical Front of the western North Pacific in an eddy‐resolving ocean general circulation model

Latitude of Eastward Jet Prematurely Separated from the Western Boundary in a Two-Layer Quasigeostrophic Model

Argo data assimilation and its effect on climate state estimation and forecasting in the western North Pacific using a coupled model

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