Differential Formation and Circulation of North Pacific Central Mode Water

2005 ◽  
Vol 35 (11) ◽  
pp. 1997-2011 ◽  
Author(s):  
Eitarou Oka ◽  
Toshio Suga
Keyword(s):  
North Pacific ◽  
World Ocean ◽  
Subtropical Gyre ◽  
Mode Water ◽  
Formation Region ◽  
The North ◽  
Central Mode Water ◽  
Central Mode ◽  
The Kuroshio ◽  
The North Pacific

Abstract A repeat hydrographic section along 165°E was analyzed to verify a westward extension of the formation region of the North Pacific Ocean Central Mode Water (CMW) suggested by previous synoptic observations, and to investigate the relation between the formation region and thermohaline fronts. The CMW formation region extends at least as far west as 155°E, much farther than recognized in a previous study based on climatology. It is located in two interfrontal regions between the Kuroshio Extension front and the Kuroshio Bifurcation front (KBF), and between the KBF and the subarctic front, where two types of CMW—namely, the lighter variety with potential density of 25.8–26.2 kg m−3 and the denser one of 26.3–26.4 kg m−3—are formed. How this differential formation of CMW is reflected in its gyrewide distribution was examined using one-time sections of the World Ocean Circulation Experiment (WOCE) Hydrographic Program in the North Pacific. The main circulation paths of the two types of CMW diverge east of the date line; the lighter variety is located in the inner part of the eastern subtropical gyre, and the denser variety is located in the outer part. These results demonstrate that the frontal structure around the northern boundary of the subtropical gyre, particularly the existence of KBF, is essential in determining the properties and the gyrewide distribution of CMW.

scholarly journals Distributions of mixed layer properties in North Pacific water mass formation areas: comparison of Argo floats and World Ocean Atlas 2001

Ocean Science ◽  
2006 ◽  
Vol 2 (1) ◽  
pp. 61-70 ◽  
Author(s):  
F. M. Bingham ◽  
T. Suga
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
World Ocean ◽  
Water Masses ◽  
Mode Water ◽  
The North ◽  
Central Mode Water ◽  
Central Mode ◽  
World Ocean Atlas ◽  
The North Pacific

Abstract. Winter mixed layer characteristics in the North Pacific Ocean are examined and compared between Argo floats in 2006 and the World Ocean Atlas 2001 (WOA01) climatology for a series of named water masses, North Pacific Tropical Water (NPTW), Eastern Subtropical Mode Water (ESTMW), North Pacific Subtropical Mode Water (NPSTMW), Light Central Mode Water (LCMW) and Dense Central Mode Water (DCMW). The WOA01 is found to be in good agreement with the Argo data in terms of water mass volumes, average temperature-salinity (T-S) properties, and outcrop areas. The exception to this conclusion is for the central mode waters, DCMW and LCMW, whose outcropping is shown to be much more intermittent than is apparent in the WOA01 and whose T-S properties vary from what is shown in the WOA01. Distributions of mixed layer T-S properties measured by floats are examined within the outcropping areas defined by the WOA01 and show some shifting of T-S characteristics within the confines of the named water masses. In 2006, all the water masses were warmer than climatology on average, with a magnitude of about 0.5°C. The NPTW, NPSTMW and LCMW were saltier than climatology and the ESTMW and DCMW fresher, with magnitudes of about 0.05. In order to put these results into context, differences between Argo and WOA01 were examined over the North Pacific between 20 and 45° N. A large-scsale warming and freshening is seen throughout this area, except for the western North Pacific, where results were more mixed.

scholarly journals Interdecadal temperature variations in the North Pacific Central Mode Water simulated by an OGCM

2004 ◽  
Vol 60 (5) ◽  
pp. 865-877 ◽  
Author(s):  
Shigeki Hosoda ◽  
Shang-Ping Xie ◽  
Kensuke Takeuchi ◽  
Masami Nonaka
Keyword(s):  
North Pacific ◽  
Mode Water ◽  
Temperature Variations ◽  
The North ◽  
Central Mode Water ◽  
Central Mode ◽  
The North Pacific

Interannual Variation of Annual Subduction Rate in the North Pacific Estimated from a Gridded Argo Product

2015 ◽  
Vol 45 (9) ◽  
pp. 2276-2293 ◽  
Author(s):  
Katsuya Toyama ◽  
Aiko Iwasaki ◽  
Toshio Suga
Keyword(s):  
Pacific Decadal Oscillation ◽  
North Pacific ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Central Mode Water ◽  
The Pacific ◽  
Central Mode ◽  
Subduction Rate ◽  
The North Pacific

AbstractSpatiotemporal variability of the subduction rate in the North Pacific from 2005 to 2012 is examined based on the Argo observational data. The subduction rate in the subtropical North Pacific varies significantly from year to year between 25 and 50 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1), and it is well correlated with the Pacific decadal oscillation. The temporal change of the subduction rate is largely determined by that of the late winter mixed layer depth through the lateral induction term. The increase (decrease) in the subduction rate in the subtropical mode water areas accompanies densification (lightening) of the mode density class of the subducted water. The subduction rate variability in the central mode water and eastern subtropical mode water regions is anticorrelated as found in the previous study using the output from an ocean GCM. The subduction rate in the central mode water density range changes dramatically, which is very large in 2005 and 2010 but almost disappears in 2009. The subduction rate variability in the western subtropical mode water regions seems to be correlated with the Pacific decadal oscillation with a lag of a few years.

Weakening and Poleward Shifting of the North Pacific Subtropical Fronts from 1980 to 2018

2021 ◽  
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Subtropical Gyre ◽  
Hadley Cell ◽  
North Pacific Subtropical Gyre ◽  
Mode Water ◽  
Mode Waters ◽  
The North ◽  
The North Pacific ◽  
Subtropical Fronts

Abstract Recent evidence shows that the North Pacific subtropical gyre, the Kuroshio Extension (KE) and Oyashio Extension (OE) fronts have moved poleward in the past few decades. However, changes of the North Pacific Subtropical Fronts (STFs), anchored by the North Pacific subtropical countercurrent in the southern subtropical gyre, remain to be quantified. By synthesizing observations, reanalysis, and eddy-resolving ocean hindcasts, we show that the STFs, especially their eastern part, weakened (20%±5%) and moved poleward (1.6°±0.4°) from 1980 to 2018. Changes of the STFs are modified by mode waters to the north. We find that the central mode water (CMW) (180°-160°W) shows most significant weakening (18%±7%) and poleward shifting (2.4°±0.9°) trends, while the eastern part of the subtropical mode water (STMW) (160°E-180°) has similar but moderate changes (10% ± 8%; 0.9°±0.4°). Trends of the western part of the STMW (140°E-160°E) are not evident. The weakening and poleward shifting of mode waters and STFs are enhanced to the east and are mainly associated with changes of the northern deep mixed layers and outcrop lines—which have a growing northward shift as they elongate to the east. The eastern deep mixed layer shows the largest shallowing trend, where the subduction rate also decreases the most. The mixed layer and outcrop line changes are strongly coupled with the northward migration of the North Pacific subtropical gyre and the KE/OE jets as a result of the poleward expanded Hadley cell, indicating that the KE/OE fronts, mode waters, and STFs change as a whole system.

“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.

Formation and Subduction of Central Mode Water Based on Profiling Float Data, 2003–08

2011 ◽  
Vol 41 (1) ◽  
pp. 113-129 ◽  
Author(s):  
Eitarou Oka ◽  
Shinya Kouketsu ◽  
Katsuya Toyama ◽  
Kazuyuki Uehara ◽  
Taiyo Kobayashi ◽  
...  
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Large Scale ◽  
Kuroshio Extension ◽  
Subtropical Gyre ◽  
Late Winter ◽  
Mode Water ◽  
Central Mode Water ◽  
Winter Mixed Layer ◽  
Central Mode

Abstract Temperature and salinity data from Argo profiling floats in the North Pacific during 2003–08 have been analyzed to study the structure of winter mixed layer north of the Kuroshio Extension and the subsurface potential vorticity distribution in the subtropical gyre in relation to the formation and subduction of the central mode water (CMW). In late winter, two zonally elongated bands of deep mixed layer extend at 33°–39° and 39°–43°N, from the east coast of Japan to 160°W. These correspond to the formation region of the lighter variety of CMW (L-CMW) and that of the denser variety of CMW (D-CMW) and the recently identified transition region mode water (TRMW), respectively. In the western part of the L-CMW and D-CMW–TRMW formation regions west of 170°E, the winter mixed layer becomes deeper and lighter to the east (i.e., to the downstream). As a result, the formed mode water is reentrained into the mixed layer in the farther east in the following winter and modified to the lighter water and is thus unable to be subducted to the permanent pycnocline. In the eastern part of the formation regions between 170°E and 160°W, on the other hand, the winter mixed layer becomes shallower and lighter to the east. From these areas, the L-CMW with potential density of 25.7–26.2 kg m−3 and the D-CMW–TRMW (mostly the former) of 26.1–26.4 kg m−3 are subducted to the permanent pycnocline, and they are then advected anticyclonically in the subtropical gyre. These results imply that during the analysis period large-scale subduction to the permanent pycnocline occurs in the density range up to 26.4 kg m−3 in the open North Pacific, whereas the winter mixed layer density reaches the maximum of 26.6 kg m−3. This is supported by the vertical distribution of apparent oxygen utilization in a hydrographic section in the subtropical gyre.

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