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Author
Xu, X. ; Chassignet, E.P., Wang, F.
Title
On the variability of the Atlantic meridional overturning circulation transports in coupled CMIP5 simulations
Type
$loc['typeJournal Article']
Year
2018
Publication
Climate Dynamics
Abbreviated Journal
Clim Dyn.
Volume
51
Issue
11
Pages
6511-6531
Keywords
NAO-AMOC ; CMIP5 ; NAO index ; AMOC index ; meridional pressure gradient ; magnitude ; structure change of the NAO.
Abstract
The Atlantic meridional overturning circulation (AMOC) plays a fundamental role in the climate system, and long-term climate simulations are used to understand the AMOC variability and to assess its impact. This study examines the basic characteristics of the AMOC variability in 44 CMIP5 (Phase 5 of the Coupled Model Inter-comparison Project) simulations, using the 18 atmospherically-forced CORE-II (Phase 2 of the Coordinated Ocean-ice Reference Experiment) simulations as a reference. The analysis shows that on interannual and decadal timescales, the AMOC variability in the CMIP5 exhibits a similar magnitude and meridional coherence as in the CORE-II simulations, indicating that the modeled atmospheric variability responsible for AMOC variability in the CMIP5 is in reasonable agreement with the CORE-II forcing. On multidecadal timescales, however, the AMOC variability is weaker by a factor of more than 2 and meridionally less coherent in the CMIP5 than in the CORE-II simulations. The CMIP5 simulations also exhibit a weaker long-term atmospheric variability in the North Atlantic Oscillation (NAO). However, one cannot fully attribute the weaker AMOC variability to the weaker variability in NAO because, unlike the CORE-II simulations, the CMIP5 simulations do not exhibit a robust NAO-AMOC linkage. While the variability of the wintertime heat flux and mixed layer depth in the western subpolar North Atlantic is strongly linked to the AMOC variability, the NAO variability is not.
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$loc['no']
Call Number
COAPS @ rl18 @
Serial
981
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Author
Xu, X. ; Rhines, P.B. ; Chassignet, E.P.
Title
On Mapping the Diapycnal Water Mass Transformation of the Upper North Atlantic Ocean
Type
$loc['typeJournal Article']
Year
2018
Publication
Journal of Physical Oceanography
Abbreviated Journal
J. Phys. Oceanogr.
Volume
48
Issue
10
Pages
2233-2258
Keywords
Atmosphere-ocean interaction ; Boundary currents ; Diapycnal mixing ; Fronts ; Thermocline circulation
Abstract
Diapycnal water mass transformation is the essence behind the Atlantic meridional overturning circulation (AMOC) and the associated heat/freshwater transports. Existing studies have mostly focused on the transformation that is forced by surface buoyancy fluxes, and the role of interior mixing is much less known. This study maps the three-dimensional structure of the diapycnal transformation, both surface forced and mixing induced, using results of a high-resolution numerical model that have been shown to represent the large-scale structure of the AMOC and the North Atlantic subpolar/subtropical gyres well. The analyses show that 1) annual mean transformation takes place seamlessly from the subtropical to the subpolar North Atlantic following the surface buoyancy loss along the northward-flowing upper AMOC limb; 2) mixing, including wintertime convection and warm-season restratification by mesoscale eddies in the mixed layer and submixed layer diapycnal mixing, drives transformations of (i) Subtropical Mode Water in the southern part of the subtropical gyre and (ii) Labrador Sea Water in the Labrador Sea and on its southward path in the western Newfoundland Basin; and 3) patterns of diapycnal transformations toward lighter and denser water do not align zonally�the net three-dimensional transformation is significantly stronger than the zonally integrated, two-dimensional AMOC streamfunction (50% in the southern subtropical North Atlantic and 60% in the western subpolar North Atlantic).
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Series Editor
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ISSN
0022-3670
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Approved
$loc['no']
Call Number
COAPS @ user @
Serial
951
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Author
Zeng, L. ; Chassignet, E.P. ; Schmitt, R.W. ; Xu, X. ; Wang, D.
Title
Salinification in the South China Sea Since Late 2012: A Reversal of the Freshening Since the 1990s
Type
$loc['typeJournal Article']
Year
2018
Publication
Geophysical Research Letters
Abbreviated Journal
Geophys. Res. Lett.
Volume
45
Issue
6
Pages
2744-2751
Keywords
South China Sea ; salinification ; Argo floats ; Aquarius ; SMAP ; PDO
Abstract
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Series Editor
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ISSN
0094-8276
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Approved
$loc['no']
Call Number
COAPS @ mfield @
Serial
853
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Author
Zhang, M. ; Wu, Z. ; Qiao, F.
Title
Deep Atlantic Ocean Warming Facilitated by the Deep Western Boundary Current and Equatorial Kelvin Waves
Type
$loc['typeJournal Article']
Year
2018
Publication
Journal of Climate
Abbreviated Journal
J. Climate
Volume
31
Issue
20
Pages
8541-8555
Keywords
Ocean ; Atlantic Ocean ; Heating ; Kelvin waves ; Ocean circulation ; Oceanic variability ; EMPIRICAL MODE DECOMPOSITION ; NONSTATIONARY TIME-SERIES ; NORTH-ATLANTIC ; CLIMATE-CHANGE ; HEAT-CONTENT ; HIATUS ; VARIABILITY ; CIRCULATION ; TEMPERATURE ; PACIFIC
Abstract
Increased heat storage in deep oceans has been proposed to account for the slowdown of global surface warming since the end of the twentieth century. How the imbalanced heat at the surface has been redistributed to deep oceans remains to be elucidated. Here, the evolution of deep Atlantic Ocean heat storage since 1950 on multidecadal or longer time scales is revealed. The anomalous heat in the deep Labrador Sea was transported southward by the shallower core of the deep western boundary current (DWBC). Upon reaching the equator around 1980, this heat transport route bifurcated into two, with one continuing southward along the DWBC and the other extending eastward along a narrow strip (about 4 degrees width) centered at the equator. In the 1990s and 2000s, meridional diffusion helped to spread warming in the tropics, making the eastward equatorial warming extension have a narrow head and wider tail. The deep Atlantic Ocean warming since 1950 had overlapping variability of approximately 60 years. The results suggest that the current basinwide Atlantic Ocean warming at depths of 1000-2000 m can be traced back to the subsurface warming in the Labrador Sea in the 1950s. An inference from these results is that the increased heat storage in the twenty-first century in the deep Atlantic Ocean is unlikely to partly account for the atmospheric radiative imbalance during the last two decades and to serve as an explanation for the current warming hiatus.
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Series Editor
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Series Issue
Edition
ISSN
0894-8755
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ user @
Serial
950
Permanent link to this record
Author
Zhang, M. ; Zhang, Y. ; Shu, Q. ; Zhao, C. ; Wang, G. ; Wu, Z. ; Qiao, F.
Title
Spatiotemporal evolution of the chlorophyll a trend in the North Atlantic Ocean
Type
$loc['typeJournal Article']
Year
2018
Publication
The Science of the Total Environment
Abbreviated Journal
Sci Total Environ
Volume
612
Issue
Pages
1141-1148
Keywords
Chlorophyll a ; Dipole pattern ; Multidimensional ensemble empirical mode decomposition ; Propagation ; Spatiotemporal evolution ; The variable trend
Abstract
Analyses of the chlorophyll a concentration (chla) from satellite ocean color products have suggested the decadal-scale variability of chla linked to the climate change. The decadal-scale variability in chla is both spatially and temporally non-uniform. We need to understand the spatiotemporal evolution of chla in decadal or multi-decadal timescales to better evaluate its linkage to climate variability. Here, the spatiotemporal evolution of the chla trend in the North Atlantic Ocean for the period 1997-2016 is analyzed using the multidimensional ensemble empirical mode decomposition method. We find that this variable trend signal of chla shows a dipole pattern between the subpolar gyre and along the Gulf Stream path, and propagation along the opposite direction of the North Atlantic Current. This propagation signal has an overlapping variability of approximately twenty years. Our findings suggest that the spatiotemporal evolution of chla during the two most recent decades is part of the multidecadal variations and possibly regulated by the changes of Atlantic Meridional Overturning Circulation, whereas the mechanisms of such evolution patterns still need to be explored.
Address
First Institute of Oceanography, State Oceanic Administration, Qingdao, China; Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China; Key Laboratory of Data Analysis and Applications, State Oceanic Administration, Qingdao, China. Electronic address: qiaofl@fio.org.cn
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Thesis
Publisher
Place of Publication
Editor
Language
English
Summary Language
Original Title
Series Editor
Series Title
Abbreviated Series Title
Series Volume
Series Issue
Edition
ISSN
0048-9697
ISBN
Medium
Area
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Conference
Funding
PMID:28892858
Approved
$loc['no']
Call Number
COAPS @ mfield @
Serial
363
Permanent link to this record
Author
Zheng, Y. ; Bourassa, M. A. ; Dukhovskoy, D. S.
Title
Upper-Ocean Processes Controlling the Sea Surface Temperature in the Western Gulf of Mexico
Type
$loc['typeAbstract']
Year
2018
Publication
American Geophysical Union
Abbreviated Journal
AGU
Volume
Fall Meeting
Issue
Pages
Keywords
4299 General or miscellaneous, OCEANOGRAPHY: GENERAL
Abstract
This study examines the upper-ocean processes controlling the mixed layer temperature in the western Gulf of Mexico (GOM) through estimating the contributing terms in the heat equation, with an emphasis on eddies' role. The major heat contributing terms for the upper GOM were estimated using two ocean reanalysis datasets: an eddy-resolving HYbrid Coordinate Ocean Model (HYCOM) and a Simple Ocean Data Assimilation (SODA). Analysis of net surface heat fluxes from four datasets reveals that the long-term mean net surface heat flux cools the northern GOM and warms the southern GOM. Two regions are focused for analysis: an eddy-rich region where LCEs are energetic, and the southwestern Gulf where eddy activity is relatively weak and the features of near surface temperature differ from the eddy-rich region. An eddy-rich region in the western GOM is defined based on the eddy kinetic energy derived from satellite sea surface heights. The long-term mean horizontal heat advection causes a weak warming over most of the eddy rich region, partly attributed to the flow-temperature configuration that the long-term and seasonally mean flow is nearly parallel to the corresponding mean isotherms. By contrast, the temporal mean vertical heat advection causes a strong warming in the eddy rich region, partly balancing the cooling caused by net surface heat flux. The temporal mean eddy heat flux convergence in the western GOM, whose positive and negative values are not small at some locations, appears heterogeneous in space, resulting in a small term for the western GOM when area averaged. The persistent warm water in the southwestern Gulf is primarily caused by the net warming from net surface heat flux rather than from eddies and heat advection.
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Approved
$loc['no']
Call Number
COAPS @ user @
Serial
1007
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