Small meanders of the Kuroshio Extension and associated northward spreading of warm water: Three‐vessel simultaneous observations and an eddy‐resolving ocean model simulation

AbstractEddy–mean flow interactions along the Kuroshio Extension (KE) jet are investigated using a vorticity budget of a high-resolution ocean model simulation, averaged over a 13-yr period. The simulation explicitly resolves mesoscale eddies in the KE and is forced with air–sea fluxes representing the years 1995–2007. A mean-eddy decomposition in a jet-following coordinate system removes the variability of the jet path from the eddy components of velocity; thus, eddy kinetic energy in the jet reference frame is substantially lower than in geographic coordinates and exhibits a cross-jet asymmetry that is consistent with the baroclinic instability criterion of the long-term mean field. The vorticity budget is computed in both geographic (i.e., Eulerian) and jet reference frames; the jet frame budget reveals several patterns of eddy forcing that are largely attributed to varicose modes of variability. Eddies tend to diffuse the relative vorticity minima/maxima that flank the jet, removing momentum from the fast-moving jet core and reinforcing the quasi-permanent meridional meanders in the mean jet. A pattern associated with the vertical stretching of relative vorticity in eddies indicates a deceleration (acceleration) of the jet coincident with northward (southward) quasi-permanent meanders. Eddy relative vorticity advection outside of the eastward jet core is balanced mostly by vertical stretching of the mean flow, which through baroclinic adjustment helps to drive the flanking recirculation gyres. The jet frame vorticity budget presents a well-defined picture of eddy activity, illustrating along-jet variations in eddy–mean flow interaction that may have implications for the jet’s dynamics and cross-frontal tracer fluxes.

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A Comparison of Mesoscale Eddy Heat Fluxes from Observations and a High-Resolution Ocean Model Simulation of the Kuroshio Extension

Journal of Physical Oceanography ◽

10.1175/jpo-d-13-0150.1 ◽

2013 ◽

Vol 43 (12) ◽

pp. 2563-2570 ◽

Cited By ~ 8

Author(s):

Stuart P. Bishop ◽

Frank O. Bryan

Keyword(s):

High Resolution ◽

Model Simulation ◽

Kuroshio Extension ◽

Mesoscale Eddy ◽

Ocean Model ◽

Heat Fluxes ◽

Dynamical Mechanism ◽

Eddy Heat Flux ◽

Conversion Rates ◽

The Kuroshio

Abstract For the first time estimates of divergent eddy heat flux (DEHF) from a high-resolution (0.1°) simulation of the Parallel Ocean Program (POP) are compared with estimates made during the Kuroshio Extension System Study (KESS). The results from POP are in good agreement with KESS observations. POP captures the lateral and vertical structure of mean-to-eddy energy conversion rates, which range from 2 to 10 cm2 s−3. The dynamical mechanism of vertical coupling between the deep and upper ocean is the process responsible for DEHFs in POP and is in accordance with baroclinic instability observed in the Gulf Stream and Kuroshio Extension. Meridional eddy heat transport values are ~14% larger in POP at its maximum value. This is likely due to the more zonal path configuration in POP. The results from this study suggest that HR POP is a useful tool for estimating eddy statistics in the Kuroshio Extension region, and thereby provide guidance in the formulation and testing of eddy mixing parameterization schemes.

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Spreading of warm water from the Kuroshio Extension into the Perturbed Area

Journal of Oceanography ◽

10.1007/bf02751701 ◽

1998 ◽

Vol 54 (3) ◽

pp. 257-271 ◽

Cited By ~ 14

Author(s):

Susana Sainz-Trápaga ◽

Takashige Sugimoto

Keyword(s):

Kuroshio Extension ◽

Warm Water ◽

The Kuroshio

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Cloud Response to the Meandering Kuroshio Extension Front

Journal of Climate ◽

10.1175/jcli-d-13-00133.1 ◽

2013 ◽

Vol 26 (23) ◽

pp. 9393-9398 ◽

Cited By ~ 9

Author(s):

Hiroyuki Tomita ◽

Shang-Ping Xie ◽

Hiroki Tokinaga ◽

Yoshimi Kawai

Keyword(s):

Kuroshio Extension ◽

Lower Atmosphere ◽

Warm Water ◽

Cloud Base ◽

Cumulus Clouds ◽

The North ◽

Strong Inversion ◽

Stratocumulus Clouds ◽

The Kuroshio ◽

Kuroshio Extension Front

A unique set of observations on board research vessel (R/V) Mirai in April 2010 captured a striking cloud hole over a cold meander of the Kuroshio Extension (KE) east of Japan as corroborated by atmospheric soundings, ceilometer, shipboard radiation data, and satellite cloud images. Distinct differences were also observed between the warm meander farther to the north and warm water south of the KE. The atmosphere is highly unstable over the warm meander, promoting a well-mixed marine atmospheric boundary layer (MABL) and a layer of solid stratocumulus clouds capped by a strong inversion. Over the warm water south of the KE, MABL deepens and is decoupled from the ocean surface. Scattered cumulus clouds develop as captured by rapid variations in ceilometer-derived cloud base. The results show that the meandering KE front affects the entire MABL and the clouds. Such atmospheric response can potentially intensify the baroclinicity in the lower atmosphere.

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An examination of a multi-scale three-dimensional variational data assimilation scheme in the Kuroshio Extension using the naval coastal ocean model

Continental Shelf Research ◽

10.1016/j.csr.2013.11.009 ◽

2014 ◽

Vol 73 ◽

pp. 41-48 ◽

Cited By ~ 8

Author(s):

Philip A. Muscarella ◽

M.J. Carrier ◽

H.E. Ngodock

Keyword(s):

Data Assimilation ◽

Kuroshio Extension ◽

Three Dimensional ◽

Coastal Ocean ◽

Ocean Model ◽

Variational Data Assimilation ◽

Multi Scale ◽

Coastal Ocean Model ◽

The Kuroshio ◽

Assimilation Scheme

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Seasonal Variability in Warm-Water Inflow toward Kangerdlugssuaq Fjord

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0202.1 ◽

2017 ◽

Vol 47 (7) ◽

pp. 1685-1699 ◽

Cited By ~ 6

Author(s):

Renske Gelderloos ◽

Thomas W. N. Haine ◽

Inga M. Koszalka ◽

Marcello G. Magaldi

Keyword(s):

Seasonal Variability ◽

Model Simulation ◽

Ocean Model ◽

Water Masses ◽

Warm Water ◽

The Arctic ◽

Seasonal Temperature ◽

Temperature Variations ◽

Denmark Strait ◽

Regional Ocean Model

AbstractSeasonal variability in pathways of warm-water masses toward the Kangerdlugssuaq Fjord (KF)–Glacier (KG) system, southeast Greenland, is investigated by backtracking Lagrangian particles seeded at the fjord mouth in a high-resolution regional ocean model simulation in the ice-free and the ice-covered seasons. The waters at KF are a mixture of Atlantic-origin water advected from the Irminger Basin [Faxaflói (FF)], the deep waters from the Denmark Strait, and the waters from the Arctic Ocean, both represented by the Kögur section (KO). Below 200-m depth, the warm water is a mixture of FF and KO water masses and is warmer in winter than in summer. The authors find that seasonal differences in pathways double the fraction of FF particles in winter, causing the seasonal warming and salinification. Seasonal temperature variations at the upstream sections (FF and KO) have a negligible impact on temperature variations near the fjord. Successful monitoring of heat flux to the fjord therefore needs to take place close to the fjord and cannot be inferred from upstream conditions.

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Response of the Kuroshio Extension to Rossby Waves Associated with the 1970s Climate Regime Shift in a High-Resolution Ocean Model*

Journal of Climate ◽

10.1175/jcli3449.1 ◽

2005 ◽

Vol 18 (15) ◽

pp. 2979-2995 ◽

Cited By ~ 52

Author(s):

Bunmei Taguchi ◽

Shang-Ping Xie ◽

Humio Mitsudera ◽

Atsushi Kubokawa

Keyword(s):

Boundary Layer ◽

High Resolution ◽

Regime Shift ◽

Rossby Waves ◽

Kuroshio Extension ◽

Ocean Model ◽

Western Boundary ◽

Climate Regime ◽

Climate Regime Shift ◽

The Kuroshio

Abstract The response of the Kuroshio Extension (KE) to large-scale Rossby waves remotely excited by wind stress changes associated with the 1970s climate regime shift is studied using a high-resolution regional ocean model. Two ensemble simulations are conducted: The control run uses monthly climatological forcing while, in the second ensemble, anomalous forcing is imposed at the model eastern boundary around 165°E derived from a hindcast of decadal changes in subsurface temperature and salinity using a coarser-resolution model of the Pacific basin. Near the KE, ocean adjustment deviates strongly from the linear Rossby wave dynamics. Most notably, the eastward acceleration of the KE is much narrower in meridional extent than that associated with the incoming Rossby waves imposed on the eastern boundary. This KE acceleration is associated with an enhanced potential vorticity (PV) gradient across the front that is consistent with the inertial western boundary layer theory: the arrival of the Rossby waves at the western boundary causes the eastward current to accelerate, leading to enhanced advection of low (high) PV water of subtropical (subarctic) origin along the western boundary layer. The meridional dipole of PV anomalies results in a pair of anomalous recirculations with a narrow eastward jet in between. A three-layer quasigeostrophic model is used to demonstrate this inertial adjustment mechanism. Finally, transient eddy activity increases significantly and the eddy momentum transport acts to strengthen the mean flow response. The result that ocean physical response to broad-scale atmospheric forcing is large near the KE front has important implications for fisheries research.

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Predictability and error growth dynamics of the Kuroshio Extension state transition process in an eddy-resolving regional ocean model

Ocean Modelling ◽

10.1016/j.ocemod.2020.101659 ◽

2020 ◽

Vol 153 ◽

pp. 101659

Author(s):

Yu Geng ◽

Qiang Wang ◽

Mu Mu ◽

Kun Zhang

Keyword(s):

State Transition ◽

Kuroshio Extension ◽

Growth Dynamics ◽

Transition Process ◽

Ocean Model ◽

Error Growth ◽

Regional Ocean Model ◽

The Kuroshio

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Isopycnal Eddy Diffusivities and Critical Layers in the Kuroshio Extension from an Eddying Ocean Model

Journal of Physical Oceanography ◽

10.1175/jpo-d-13-0258.1 ◽

2014 ◽

Vol 44 (8) ◽

pp. 2191-2211 ◽

Cited By ~ 18

Author(s):

Ru Chen ◽

Julie L. McClean ◽

Sarah T. Gille ◽

Alexa Griesel

Keyword(s):

Kuroshio Extension ◽

Baroclinic Instability ◽

Ocean Model ◽

Critical Layer ◽

Eddy Diffusivities ◽

Clustering Approach ◽

Critical Layers ◽

Recirculation Gyre ◽

The Kuroshio ◽

Stream Direction

Abstract High spatial resolution isopycnal diffusivities are estimated in the Kuroshio Extension (KE) region (28°–40°N, 120°–190°E) from a global ° Parallel Ocean Program (POP) simulation. The numerical float tracks are binned using a clustering approach. The number of tracks in each bin is thus roughly the same leading to diffusivity estimates that converge better than those in bins defined by a regular geographic grid. Cross-stream diffusivities are elevated in the southern recirculation gyre region, near topographic obstacles and downstream in the KE jet, where the flow has weakened. Along-stream diffusivities, which are much larger than cross-stream diffusivities, correlate well with the magnitudes of eddy velocity. The KE jet suppresses cross-stream mixing only in some longitude ranges. This study estimates the critical layer depth both from linear local baroclinic instability analysis and from eddy phase speeds in the POP model using the Radon transform. The latter is a better predictor of large mixing length in the cross-stream direction. Critical layer theory is most applicable in the intense jet regions away from topography.

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