scholarly journals Impact of Remote Reemergence of the Subtropical Mode Water on Winter SST Variation in the Central North Pacific

2007 ◽  
Vol 20 (2) ◽  
pp. 173-186 ◽  
Author(s):  
Shusaku Sugimoto ◽  
Kimio Hanawa
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Heat Content ◽  
Aleutian Low ◽  
Mode Water ◽  
The North ◽  
Winter Mixed Layer ◽  
The North Pacific ◽  
Low Activity ◽  
Central North Pacific

Abstract Using long-term datasets of sea surface temperature (SST), core-layer temperature (CLT) of the North Pacific subtropical mode water (NPSTMW), and the North Pacific index, an impact of remote reemergence of NPSTMW on winter SST variation in the central North Pacific is quantitatively investigated. A running correlation analysis between CLT and winter SST in the remote reemergence area clearly shows that an occurrence of remote reemergence of NPSTMW strongly depends on the specific time period: occurrence period and nonoccurrence period. It is found that background conditions, such as formation rate of NPSTMW, winter mixed layer depth, ocean heat content, and buoyancy flux, play a crucial role in the period-dependent remote reemergence. In the occurrence (nonoccurrence) periods, since a large positive (negative) upper-ocean heat content anomaly is located around the central North Pacific, a deeper (shallower) winter mixed layer is formed in both the formation area and the reemergence area of NPSTMW. Therefore, a large (small) amount of NPSTMW is formed, and consequently the advective part of NPSTMW is preserved (dissipated) from (because of) a vigorous mixing due to salt-finger-type convection. In addition, larger (less) oceanic buoyancy loss contributes to an occurrence of reemergence. These are favorable (unfavorable) conditions for persistence of thermal anomalies and occurrence of reemergence in the central North Pacific. Using a multiple regression analysis, it is shown that remote reemergence gives a significant impact to an equivalent degree to the surface thermal forcing related with the Aleutian low activity on winter SST variation during the occurrence periods, while there is no significant contribution to SST variation during the nonoccurrence periods. It is also shown that the period-dependent reemergence closely connects with the Aleutian low activity with a lag of 6 to 8 yr, that is, the spinup/spindown of the subtropical gyre.

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.

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 The North Pacific Climatology of Winter Mixed Layer and Mode Waters

2004 ◽  
Vol 34 (1) ◽  
pp. 3-22 ◽  
Author(s):  
Toshio Suga ◽  
Kazunori Motoki ◽  
Yoshikazu Aoki ◽  
Alison M. Macdonald
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Mode Waters ◽  
The North ◽  
Winter Mixed Layer ◽  
The North Pacific

scholarly journals Chlorofluorocarbons (CFCs) in the North Pacific Central Mode Water: Possibility of under-saturation of CFCs in the wintertime mixed layer

2004 ◽  
Vol 38 (6) ◽  
pp. 643-650 ◽  
Author(s):  
Takayuki Tokieda ◽  
Masao Ishii ◽  
Tamaki Yasuda ◽  
Kazutaka Enyo
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Mode Water ◽  
The North ◽  
Central Mode Water ◽  
Central Mode ◽  
The North Pacific

scholarly journals The Transition Region Mode Water of the North Pacific and Its Rapid Modification

2011 ◽  
Vol 41 (9) ◽  
pp. 1639-1658 ◽  
Author(s):  
Hiroko Saito ◽  
Toshio Suga ◽  
Kimio Hanawa ◽  
Nobuyuki Shikama
Keyword(s):  
Transition Region ◽  
Mixed Layer ◽  
North Pacific ◽  
Water Masses ◽  
Mode Water ◽  
Formation Region ◽  
Argo Float ◽  
The North ◽  
Modification Process ◽  
The North Pacific

Abstract Using Argo float data, this study examined the formation region, spatial distribution, and modification of transition region mode water (TRMW), which is a recently identified pycnostad in the subtropical–subarctic transition region of the North Pacific, the basin-scale boundary region between subtropical and subarctic water masses. Analyses of the formation fields of water masses within and around the transition region reveal that TRMW forms in a wide area from the western to central transition region and is separated from the denser variety of central mode water (D-CMW) to the south by a temperature and salinity front. TRMW has temperatures of 4°–9°C and salinities of 33.3–34.0, making it colder and fresher than D-CMW. TRMW has a density range of 26.3–26.6 σθ, and thick TRMW is widely distributed in the transition region. However, the range of the T–S properties at TRMW cores is substantially reduced downstream within 10°–20° longitude from the formation region by gradually losing its fresh and cold side. It is also demonstrated that a major part of TRMW of 26.4–26.6 σθ is entrained into the mixed layer in the following winter. Quasi-Lagrangian observation by an isopycnal-following Argo float demonstrates that the double-diffusive salt-finger convection plausibly causes not only rapid erosion of the TRMW pycnostads but also an increase of salinity and temperature at the TRMW cores, at least to some degree. It is demonstrated that strong salt fingering within TRMW is probably caused by geostrophic currents with vertical shear crossing the density-compensating T–S front that brings warm and saline water to the upper TRMW and creates instability in the salinity stratification. This modification process could explain why water that is subducted from the transition region and constitutes the pycnocline of the subtropical gyre in the North Pacific has different T–S properties from the winter mixed layer of the transition region. This knowledge about the modification process of subducted water in the transition region would help to model the permanent pycnocline structure more realistically and to clarify how large signals of decadal and multidecadal variability of sea surface temperature in this region are propagated into the ocean interior.

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 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.

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