Role of the ocean mixed layer processes in the response of the North Pacific winter SST and MLD to global warming in CGCMs

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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Upper-Ocean Mixed Layer and Wintertime Sea Surface Temperature Anomalies in the North Pacific

Journal of Climate ◽

10.1175/jcli3616.1 ◽

2006 ◽

Vol 19 (2) ◽

pp. 300-307 ◽

Cited By ~ 11

Author(s):

Tomohiko Tomita ◽

Masami Nonaka

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

Mixed Layer ◽

North Pacific ◽

Sea Surface ◽

Upper Ocean ◽

Ocean Mixed Layer ◽

The North ◽

The Impact ◽

The North Pacific

Abstract In the North Pacific, the wintertime sea surface temperature anomaly (SSTA), which is represented by March (SSTAMar), when the upper-ocean mixed layer depth (hMar) reaches its maximum, is formed by the anomalous surface forcing from fall to winter (S′). As a parameter of volume, hMar has a potential to modify the impact of S′ on SSTAMar. Introducing an upper-ocean heat budget equation, the present study identifies the physical relationship among the spatial distributions of hMar, S′, and SSTAMar. The long-term mean of hMar adjusts the spatial distribution of SSTAMar. Without the adjustment, the impact of S′ on SSTAMar is overestimated where the hMar mean is deep. Since hMar is partially due to seawater temperature, it leads to nonlinearity between the S′ and the SSTAMar. When the SSTAMar is negative (positive), the sensitivity to S′ is impervious (responsive) with the deepening (shoaling) of the hMar compared to the linear sensitivity. The thermal impacts from the ocean to the atmosphere might be underestimated under the assumption of the linear relationship.

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Response of the ocean mixed layer depth to global warming and its impact on primary production: a case for the North Pacific Ocean

ICES Journal of Marine Science ◽

10.1093/icesjms/fsr064 ◽

2011 ◽

Vol 68 (6) ◽

pp. 996-1007 ◽

Cited By ~ 25

Author(s):

Chan Joo Jang ◽

Jisoo Park ◽

Taewook Park ◽

Sinjae Yoo

Keyword(s):

Global Warming ◽

Pacific Ocean ◽

Primary Production ◽

Mixed Layer ◽

North Pacific ◽

North Pacific Ocean ◽

Mixed Layer Depth ◽

Layer Depth ◽

The North ◽

The North Pacific

Abstract Jang, C. J., Park, J., Park, T., and Yoo, S. 2011. Response of the ocean mixed layer depth to global warming and its impact on primary production: a case for the North Pacific Ocean. – ICES Journal of Marine Science, 68: 996–1007. This study investigates changes in the mixed layer depth (MLD) in the North Pacific Ocean in response to global warming and their impact on primary production by comparing outputs from 11 models of the coupled model intercomparison projects phase 3. The MLD in the 21st century decreases in most regions of the North Pacific, whereas the spatial pattern of the MLD is nearly unchanged. The overall shoaling results in part from intensified upper-ocean stratification caused by both surface warming and freshening. A significant MLD decrease (>30 m) is found in the Kuroshio extension (KE), which is predominantly driven by reduced surface cooling, caused by weakening of wind. Associated with the mixed layer shoaling in the KE, the primary production component resulting from seasonal vertical mixing will be reduced by 10.7–40.3% (ranges of medians from 11 models) via decreased nitrate fluxes from below it. Spring blooms in most models are projected to initiate earlier in the KE by 0–13 d (ranges of medians from 11 models). Despite the overall trends, the magnitude of changes in primary production and timing of spring blooms are quite different depending on models and latitudes.

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

Journal of Physical Oceanography ◽

10.1175/jpo-d-21-0170.1 ◽

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.

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3D Structure of Striations in the North Pacific

Journal of Physical Oceanography ◽

10.1175/jpo-d-21-0076.1 ◽

2021 ◽

Author(s):

YU ZHANG ◽

YU PING GUAN ◽

RUI XIN HUANG

Keyword(s):

North Pacific ◽

3D Structure ◽

Three Dimensional ◽

Vertical Plane ◽

Dimensional Structure ◽

The North ◽

Layer Analysis ◽

Fluid Potential ◽

The North Pacific

AbstractOcean striations are composed of alternating quasi-zonal band-like flows; this kind of organized structure of currents be found in all world’s oceans and seas. Previous studies have mainly been focused on the mechanisms of their generation and propagation. This study uses the spatial high-pass filtering to obtain the three-dimensional structure of ocean striations in the North Pacific in both the z-coordinate and σ-coordinate based on 10-yr averaged SODA3 data. First, we identify an ideal-fluid potential density domain where the striations are undisturbed by the surface forcing and boundary effects. Second, using the isopycnal layer analysis, we show that on isopycnal surfaces the orientations of striations nearly follow the potential vorticity (PV) contours, while in the meridional-vertical plane the central positions of striations are generally aligned with the latitude of zero gradient of the relative PV. Our analysis provides a simple dynamical interpretation and better understanding for the role of ocean striations.

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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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The North Pacific Pacemaker Effect on Historical ENSO and Its Mechanisms

Journal of Climate ◽

10.1175/jcli-d-19-0040.1 ◽

2019 ◽

Vol 32 (22) ◽

pp. 7643-7661 ◽

Cited By ~ 4

Author(s):

Dillon J. Amaya ◽

Yu Kosaka ◽

Wenyu Zhou ◽

Yu Zhang ◽

Shang-Ping Xie ◽

...

Keyword(s):

El Niño ◽

North Pacific ◽

El Nino ◽

Southern Oscillation ◽

Deep Convection ◽

Boreal Summer ◽

Enso Events ◽

The North ◽

The North Pacific

Abstract Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate El Niño–Southern Oscillation (ENSO), but there has been little effort to put extratropical–tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully coupled climate model to produce an ensemble of North Pacific Ocean–Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N) but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1) a wind–evaporation–SST (WES) propagating mechanism, and 2) a Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the summer deep convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial date line. On an event-by-event basis, nPOGA most closely reproduces the 2014/15 and the 2015/16 El Niños. In particular, we show that the 2015 Pacific meridional mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015/16 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal time scales.

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