“Eddy Resolving” Observation of the North Pacific Subtropical Mode Water

2011 ◽  
Vol 41 (4) ◽  
pp. 666-681 ◽  
Author(s):  
Eitarou Oka ◽  
Toshio Suga ◽  
Chiho Sukigara ◽  
Katsuya Toyama ◽  
Keishi Shimada ◽  
...  
Keyword(s):  
High Resolution ◽  
North Pacific ◽  
Kuroshio Extension ◽  
Uniform Structure ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Late Fall ◽  
The Kuroshio ◽  
The North Pacific

Abstract Hydrographic data obtained by high-resolution shipboard observations and Argo profiling floats have been analyzed to study the mesoscale structure and circulation of the North Pacific Subtropical Mode Water (STMW). The float data show that in the late winter of 2008, STMW having a temperature of approximately 18.8°, 17.7°, and 16.6°C formed west of 140°E, at 140°–150°E, and east of 150°E, respectively, in the recirculation gyre south of the Kuroshio Extension. After spring, the newly formed STMW gradually shift southward, decreasing in thickness. Simultaneously, the STMWs of 16.6° and 17.7°C are gradually stirred and then mixed in terms of properties. In late fall, they seem to be integrated to form a single group of STMWs having a temperature centered at 17.2°C. Such STMW circulation in 2008 is much more turbulent than that in 2006, which was investigated in a previous study. The difference between the two years is attributed to the more variable state of the Kuroshio Extension in 2008, associated with stronger eddy activities in the STMW formation region, which enhance the eddy transport of STMW. High-resolution shipboard observations were carried out southeast of Japan at 141°–147°E in the early fall of 2008. To the south of the Kuroshio Extension, STMW exists as a sequence of patches with a horizontal scale of 100–200 km, whose thick portions correspond well to the mesoscale deepening of the permanent pycnocline. The western (eastern) hydrographic sections are occupied mostly by the 17.7°C (16.6°C) STMW, within which the 16.6°C (17.7°C) STMW exists locally, mostly at locations where both the permanent pycnocline depth and the STMW thickness are maximum. This structure implies that the STMW patches are transported away from their respective formation sites, corresponding to a shift in the mesoscale anticyclonic circulations south of the Kuroshio Extension. Furthermore, 20%–30% of the observed STMW pycnostads have two or three potential vorticity minima, mostly near temperatures of 16.6° and 17.7°C. The authors presume that such a structure formed as a result of the interleaving of the 16.6° and 17.7°C STMWs after they are stirred by mesoscale circulations, following which they are vertically mixed to form the 17.2°C STMW observed in late fall. These results indicate the importance of horizontal processes in destroying the vertically uniform structure of STMW after spring, particularly when the Kuroshio Extension is in a variable state.

scholarly journals Sensitivity of the Ventilation Process in the North Pacific to Eddy-Induced Tracer Transport*

2006 ◽  
Vol 36 (10) ◽  
pp. 1895-1911 ◽  
Author(s):  
Takahiro Endoh ◽  
Yanli Jia ◽  
Kelvin J. Richards
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Kuroshio Extension ◽  
Tracer Transport ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Subduction Rate ◽  
The Kuroshio ◽  
The North Pacific

Abstract A coarse-resolution isopycnal model coupled with a bulk mixed layer model is used to examine the effect of isopycnal thickness diffusion, which parameterizes the subgrid-scale eddy-induced tracer transport, on ventilation of the North Pacific Ocean. Three numerical experiments with thickness diffusivities of 0 m2 s−1 and around 500 and 2000 m2 s−1 are carried out. The model successfully reproduces a deep winter mixed layer in the subarctic North Pacific, leading to well-formed mode waters and the subtropical countercurrent in the experiment with thickness diffusivity around 500 m2 s−1. The annual-mean subduction rate has peaks at densities of 25.0–25.4 and 26.4 σθ. The former peak spans the densities of North Pacific Subtropical Mode Water and North Pacific Eastern Subtropical Mode Water, whereas the latter peak is centered near the density of North Pacific Central Mode Water. The annual mean obduction rate also has the former peak and a slight enhancement corresponding to the latter peak. The Kuroshio plays a crucial role in obduction of North Pacific Subtropical Mode Water by transferring it northward from the permanent pycnocline to the seasonal pycnocline around the Kuroshio Extension, the importance of which has been overlooked in previous studies. In contrast to the simple expectation that the eddy-induced tracer transport enhances the ventilation process, stronger circulation with lower thickness diffusion increases the annual-mean subduction rate by carrying the subducted water quickly away from the seasonal pycnocline into the permanent pycnocline, as well as the annual-mean obduction rate by transferring much water from the permanent pycnocline to the seasonal pycnocline. As thickness diffusivity increases, the former peaks in the subduction and obduction rates occur at lighter densities, whereas the latter peak in the subduction rate is shifted toward higher densities.

scholarly journals Poleward Shift of the Kuroshio Extension Front and its Impact on the North Pacific Subtropical Mode Water in the Recent Decades

2020 ◽  
Author(s):  
Baolan Wu ◽  
Xiaopei Lin ◽  
Lisan Yu
Keyword(s):  
North Pacific ◽  
Kuroshio Extension ◽  
Mixed Layer Depth ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Poleward Shift ◽  
Subduction Rate ◽  
The Kuroshio ◽  
The North Pacific

AbstractMeridional shift of the Kuroshio Extension (KE) front and changes in the formation of the North Pacific Subtropical Mode Water (STMW) during 1979-2018 are reported. The surface-to-subsurface structure of the KE front averaged over 142°E-165°E has shifted poleward at a rate of ~ 0.23±0.16° per decade. The shift was caused mainly by the poleward shift of the downstream KE front (153°E-165°E, ~ 0.41±0.29° per decade), barely by the upstream KE front (142°E-153°E). The long-term shift trend of the KE front showed two distinct behaviors before and after 2002. Before 2002, the surface KE front moved northward with a faster rate than the subsurface. After 2002, the surface KE front showed no obvious trend, but the subsurface KE front continued to move northward. The ventilation zone of the STMW, defined by the area between 16°C and 18°C isotherms or between 25 kg m-3 and 25.5 kg m-3 isopycnals, contracted and displaced northward with a shoaling of the mixed layer depth (hm) before 2002 when the KE front moved northward. The STMW subduction rate was reduced by 0.76 Sv (63%) during 1979-2018, most of which occurred before 2002. Of the three components affecting the total subduction rate, the temporal induction ( −∂hm/∂t ) was dominant accounting for 91% of the rate reduction, while the vertical pumping (−wmb) amounted to 8% and the lateral induction (−umb · ∇hm) was insignificant. The reduced temporal induction was attributed to both the contracted ventilation zone and the shallowed hm that were incurred by the poleward shift of KE front.

scholarly journals Decadal-scale variability of the North Pacific subtropical mode water and its influence on the pycnocline observed along 137°E

2020 ◽  
Author(s):  
Fumiaki Kobashi ◽  
Toshiya Nakano ◽  
Naoto Iwasaka ◽  
Tomomichi Ogata
Keyword(s):  
North Pacific ◽  
Numerical Models ◽  
Kuroshio Extension ◽  
Japan Meteorological Agency ◽  
Mode Water ◽  
Substantial Impact ◽  
Subtropical Mode Water ◽  
The North ◽  
Decadal Scale ◽  
The North Pacific

AbstractDecadal-scale variability of the North Pacific subtropical mode water (STMW) and its influence on the pycnocline are examined by analyzing Japan Meteorological Agency (JMA) repeat hydrographic observations along the 137°E meridian from 1972 to 2019, with a particular focus on the summer season when the seasonal upper pycnocline develops above the STMW. The STMW appears between 20° and 32°N at 137°E, with the thickness varying on decadal timescales of approximately 9–15 years. Argo float observations suggest that the observed change in the STMW thickness originates in the wintertime mixed layer south of the Kuroshio Extension in the preceding year. The STMW has a substantial impact on the pycnocline. The presence of thick STMW shoals the upper pycnocline, occasionally concurrent with the deepening of the lower main pycnocline. The change is robust in the upper pycnocline, where the heaving of isopycnal surfaces occurs with density anomalies up near the surface. The subtropical front (STF) at subsurface depths, which is associated with a northward shoaling of the upper pycnocline and is maintained by the STMW in the climatology, also changes on decadal timescales. A thick STMW increases the northward shoaling of the upper pycnocline and intensifies the STF. On decadal timescales, the STF variations are accounted for by the STMW-induced change in the upper pycnocline slope. The change in the STF due to mode waters is consistent with previous findings from numerical models.

scholarly journals Variations of the North Pacific Subtropical Mode Water from Direct Observations

2014 ◽  
Vol 27 (8) ◽  
pp. 2842-2860 ◽  
Author(s):  
Luc Rainville ◽  
Steven R. Jayne ◽  
Meghan F. Cronin
Keyword(s):  
North Pacific ◽  
Seasonal Cycle ◽  
Kuroshio Extension ◽  
Heat Content ◽  
Mesoscale Eddies ◽  
Mode Water ◽  
The North ◽  
Recirculation Gyre ◽  
The Kuroshio ◽  
The North Pacific

Abstract Mooring measurements from the Kuroshio Extension System Study (June 2004–June 2006) and from the ongoing Kuroshio Extension Observatory (June 2004–present) are combined with float measurements of the Argo network to study the variability of the North Pacific Subtropical Mode Water (STMW) across the entire gyre, on time scales from days, to seasons, to a decade. The top of the STMW follows a seasonal cycle, although observations reveal that it primarily varies in discrete steps associated with episodic wind events. The variations of the STMW bottom depth are tightly related to the sea surface height (SSH), reflecting mesoscale eddies and large-scale variations of the Kuroshio Extension and recirculation gyre systems. Using the observed relationship between SSH and STMW, gridded SSH products and in situ estimates from floats are used to construct weekly maps of STMW thickness, providing nonbiased estimates of STMW total volume, annual formation and erosion volumes, and seasonal and interannual variability for the past decade. Year-to-year variations are detected, particularly a significant decrease of STMW volume in 2007–10 primarily attributable to a smaller volume formed. Variability of the heat content in the mode water region is dominated by the seasonal cycle and mesoscale eddies; there is only a weak link to STMW on interannual time scales, and no long-term trends in heat content and STMW thickness between 2002 and 2011 are detected. Weak lagged correlations among air–sea fluxes, oceanic heat content, and STMW thickness are found when averaged over the northwestern Pacific recirculation gyre region.

scholarly journals On the Relationship between Synoptic Wintertime Atmospheric Variability and Path Shifts in the Gulf Stream and the Kuroshio Extension

2009 ◽  
Vol 22 (12) ◽  
pp. 3177-3192 ◽  
Author(s):  
Terrence M. Joyce ◽  
Young-Oh Kwon ◽  
Lisan Yu
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Western Boundary ◽  
Atmospheric Variability ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Coherent, large-scale shifts in the paths of the Gulf Stream (GS) and the Kuroshio Extension (KE) occur on interannual to decadal time scales. Attention has usually been drawn to causes for these shifts in the overlying atmosphere, with some built-in delay of up to a few years resulting from propagation of wind-forced variability within the ocean. However, these shifts in the latitudes of separated western boundary currents can cause substantial changes in SST, which may influence the synoptic atmospheric variability with little or no time delay. Various measures of wintertime atmospheric variability in the synoptic band (2–8 days) are examined using a relatively new dataset for air–sea exchange [Objectively Analyzed Air–Sea Fluxes (OAFlux)] and subsurface temperature indices of the Gulf Stream and Kuroshio path that are insulated from direct air–sea exchange, and therefore are preferable to SST. Significant changes are found in the atmospheric variability following changes in the paths of these currents, sometimes in a local fashion such as meridional shifts in measures of local storm tracks, and sometimes in nonlocal, broad regions coincident with and downstream of the oceanic forcing. Differences between the North Pacific (KE) and North Atlantic (GS) may be partly related to the more zonal orientation of the KE and the stronger SST signals of the GS, but could also be due to differences in mean storm-track characteristics over the North Pacific and North Atlantic.

Enhanced warming of the subtropical mode water in the North Pacific and North Atlantic

2017 ◽  
Vol 7 (9) ◽  
pp. 656-658 ◽  
Author(s):  
Shusaku Sugimoto ◽  
Kimio Hanawa ◽  
Tomowo Watanabe ◽  
Toshio Suga ◽  
Shang-Ping Xie
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
The North Pacific

Climatology and decadal variations in multicore structure of the North Pacific subtropical mode water

2017 ◽  
Vol 122 (9) ◽  
pp. 7506-7520 ◽  
Author(s):  
Cong Liu ◽  
Shang-Ping Xie ◽  
Peiliang Li ◽  
Lixiao Xu ◽  
Wendian Gao
Keyword(s):  
North Pacific ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Decadal Variations ◽  
The North Pacific

scholarly journals Southward spreading of the Fukushima-derived radiocesium across the Kuroshio Extension in the North Pacific

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Yuichiro Kumamoto ◽  
Michio Aoyama ◽  
Yasunori Hamajima ◽  
Tatsuo Aono ◽  
Shinya Kouketsu ◽  
...  
Keyword(s):  
North Pacific ◽  
Kuroshio Extension ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific
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