The North Pacific Climatology of Winter Mixed Layer and Mode Waters

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.

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

Journal of Climate ◽

10.1175/jcli4004.1 ◽

2007 ◽

Vol 20 (2) ◽

pp. 173-186 ◽

Cited By ~ 11

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.

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Heat and salt budgets of the mixed layer around the Subarctic Front of the North Pacific Ocean

“Hot Spots” in the Climate System ◽

10.1007/978-4-431-56053-1_4 ◽

2016 ◽

pp. 59-72

Author(s):

Vincent Faure ◽

Yoshimi Kawai

Keyword(s):

Pacific Ocean ◽

Mixed Layer ◽

North Pacific ◽

North Pacific Ocean ◽

The North ◽

Subarctic Front ◽

The North Pacific

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

Ocean Science ◽

10.5194/os-2-61-2006 ◽

2006 ◽

Vol 2 (1) ◽

pp. 61-70 ◽

Cited By ~ 13

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.

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Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Climate Dynamics ◽

10.1007/s00382-015-2762-3 ◽

2015 ◽

Vol 49 (3) ◽

pp. 891-907 ◽

Cited By ~ 13

Author(s):

Takahiro Toyoda ◽

Yosuke Fujii ◽

Tsurane Kuragano ◽

Naohiro Kosugi ◽

Daisuke Sasano ◽

...

Keyword(s):

Mixed Layer ◽

North Pacific ◽

Decadal Variability ◽

The North ◽

The North Pacific

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Roles of mode waters in the formation and maintenance of central water in the North Pacific

Journal of Oceanography ◽

10.1007/s10872-011-0040-5 ◽

2011 ◽

Vol 68 (1) ◽

pp. 79-92 ◽

Cited By ~ 4

Author(s):

Katsuya Toyama ◽

Toshio Suga

Keyword(s):

North Pacific ◽

Mode Waters ◽

The North ◽

The North Pacific

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Role of North Pacific Mixed Layer in the Response of SST Annual Cycle to Global Warming

Journal of Climate ◽

10.1175/jcli-d-14-00349.1 ◽

2015 ◽

Vol 28 (23) ◽

pp. 9451-9458 ◽

Cited By ~ 3

Author(s):

Changlin Chen ◽

Guihua Wang

Keyword(s):

Global Warming ◽

Mixed Layer ◽

Annual Cycle ◽

North Pacific ◽

North Pacific Ocean ◽

Mixed Layer Depth ◽

Ecological Impacts ◽

Global Ocean ◽

The North ◽

The North Pacific

Abstract The annual cycle of sea surface temperature (SST) in the North Pacific Ocean is examined in terms of its response to global warming based on climate model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). As the global ocean warms up, the SST in the North Pacific generally tends to increase and the warming is greater in summer than in winter, leading to a significant intensification of SST annual cycle. The mixed layer temperature equation is used to examine the mechanism of this intensification. Results show that the decrease of mixed layer depth (MLD) in summer is the main reason behind the intensification of SST annual cycle. Because the MLD in summer is much shallower than that in winter, the incoming net heat flux is trapped in a thinner surface layer in summer, causing a warmer summer SST and the amplification of SST annual cycle. The change of the SST annual cycle in the North Pacific may have profound ecological impacts.

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