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Author (up) 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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Call Number COAPS @ rl18 @ Serial 981
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Author (up) Xu, X.; Chassignet, E.P.; Firing, Y.L.; Donohue, K.
Title Antarctic Circumpolar Current transport through Drake Passage: What can we learn from comparing high-resolution model results to observations? Type $loc['typeJournal Article']
Year 2020 Publication Journal of Geophysical Research: Oceans Abbreviated Journal J. Geophys. Res. Oceans
Volume 125 Issue 7 Pages
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Abstract Uncertainty exists in the time‐mean total transport of the Antarctic Circumpolar Current (ACC), the world�s strongest ocean current. The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively. In this paper, we use a realistic 1/12° global ocean simulation to interpret these observational estimates and reconcile their differences. We first show that the modeled ACC transport in the upper 1000 m is in excellent agreement with repeat shipboard acoustic Doppler current profiler (SADCP) transects and that the exponentially decaying transport profile in the model is consistent with the profile derived from repeat hydrographic data. By further comparing the model results to the cDrake and DRAKE observations, we argue that the modeled 157.3 Sv transport, i.e. approximately the average of the cDrake and DRAKE estimates, is actually representative of the time‐mean ACC transport through the Drake Passage. The cDrake experiment overestimated the barotropic contribution in part because the array undersampled the deep recirculation southwest of the Shackleton Fracture Zone, whereas the surface geostrophic currents used in the DRAKE estimate yielded a weaker near‐surface transport than implied by the SADCP data. We also find that the modeled baroclinic and barotropic transports are not correlated, thus monitoring either baroclinic or barotropic transport alone may be insufficient to assess the temporal variability of the total ACC transport.
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Call Number COAPS @ user @ Serial 1107
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Author (up) Xu, X.; Chassignet, E.P.; Johns, W.E.; Schmitz Jr, W.J.; Metzger, E.J.
Title Intraseasonal to interannual variability of the Atlantic meridional overturning circulation from eddy-resolving simulations and observations Type $loc['typeJournal Article']
Year 2014 Publication Journal of Geophysical Research: Oceans Abbreviated Journal J. Geophys. Res. Oceans
Volume 119 Issue 8 Pages 5140-5159
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Series Editor Series Title Abbreviated Series Title
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ISSN 2169-9275 ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ mfield @ Serial 152
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Author (up) Xu, X.; Chassignet, E.P.; Price, J.F.; Özgökmen, T.M.; Peters, H.
Title A regional modeling study of the entraining Mediterranean outflow Type $loc['typeJournal Article']
Year 2007 Publication Journal of Geophysical Research Abbreviated Journal J. Geophys. Res.
Volume 112 Issue C12 Pages
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Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
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ISSN 0148-0227 ISBN Medium
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Funding Approved $loc['no']
Call Number COAPS @ mfield @ Serial 420
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Author (up) 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 Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0022-3670 ISBN Medium
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Funding Approved $loc['no']
Call Number COAPS @ user @ Serial 951
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Author (up) Xu, X.; Rhines, P.B.; Chassignet, E.P.
Title Temperature-Salinity Structure of the North Atlantic Circulation and Associated Heat and Freshwater Transports Type $loc['typeJournal Article']
Year 2016 Publication Journal of Climate Abbreviated Journal J. Climate
Volume 29 Issue 21 Pages 7723-7742
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Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0894-8755 ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ mfield @ Serial 58
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Author (up) Xu, X.; Rhines, P.B.; Chassignet, E.P.; Schmitz Jr., W.J.
Title Spreading of Denmark Strait Overflow Water in the Western Subpolar North Atlantic: Insights from Eddy-Resolving Simulations with a Passive Tracer Type $loc['typeJournal Article']
Year 2015 Publication Journal of Physical Oceanography Abbreviated Journal J. Phys. Oceanogr.
Volume 45 Issue 12 Pages 2913-2932
Keywords Circulation/ Dynamics; Abyssal circulation; Boundary currents; Ocean circulation; Ocean dynamics; Potential vorticity; Topographic effects
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Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0022-3670 ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ mfield @ Serial 116
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Author (up) Xu, X.; Schmitz Jr., W.J.; Hurlburt, H.E.; Hogan, P.J.; Chassignet, E.P.
Title Transport of Nordic Seas overflow water into and within the Irminger Sea: An eddy-resolving simulation and observations Type $loc['typeJournal Article']
Year 2010 Publication Journal of Geophysical Research Abbreviated Journal J. Geophys. Res.
Volume 115 Issue C12 Pages
Keywords transport; overflow water; Nordic Seas; North Atlantic Deep Water; Irminger Sea; Reykjanes Ridge
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0148-0227 ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ mfield @ Serial 367
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Author (up) 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
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0094-8276 ISBN Medium
Area Expedition Conference
Funding Approved $loc['no']
Call Number COAPS @ mfield @ Serial 853
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Author (up) Zhao, X.; Zhou, C.; Xu, X.; Ye, R.; Tian, J.; Zhao, W.
Title Deep Circulation in the South China Sea Simulated in a Regional Model Type $loc['typeJournal Article']
Year 2019 Publication Ocean Sci. Discuss Abbreviated Journal Ocean Sci. Discuss
Volume Issue Pages
Keywords Sea Marine, Oceanography/CIMST, PacificOcean, continuous current-meter, deep circulation, deep western boundary
Abstract The South China Sea (SCS) is the largest marginal sea in the northwest Pacific Ocean. In this study, deep circulation in the SCS is investigated using results from eddy-resolving, regional simulations using the Hybrid Coordinate Ocean Model (HYCOM) verified by continuous current-meter observations. Analysis of these results provides a detailed spatial structure and temporal variability of the deep circulation in the SCS. The major features of the SCS deep circulation are a basin-scale cyclonic gyre and a concentrated deep western boundary current (DWBC). Transport of the DWBC is ∼ 2 Sv at 16.5° N with a width of ∼53 km. Flowing southwestward, the narrow DWBC becomes weaker with a wider range. The model results reveal the existence of 80- to 120-day oscillation in the deep northeastern circulation and the DWBC, which are also the areas with elevated eddy kinetic energy. This intraseasonal oscillation propagates northwestward with a velocity amplitude of ∼ 1.0 to 1.5 cm s-1. The distribution of mixing parameters in the deep SCS plays a role in both spatial structure and volume transport of the deep circulation. Compared with the northern shelf of the SCS with the Luzon Strait, deep circulation in the SCS is more sensitive to the large vertical mixing parameters of the Zhongsha Island Chain area.
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Funding Approved $loc['no']
Call Number COAPS @ user @ Serial 1013
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