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| Author | Trossman, D.S.; Arbic, B.K.; Straub, D.N.; Richman, J.G.; Chassignet, E.P.; Wallcraft, A.J.; Xu, X. | ||||
| Title | The Role of Rough Topography in Mediating Impacts of Bottom Drag in Eddying Ocean Circulation Models | Type | $loc['typeJournal Article'] | ||
| Year | 2017 | Publication | Journal of Physical Oceanography | Abbreviated Journal | J. Phys. Oceanogr. |
| Volume | 47 | Issue | 8 | Pages | 1941-1959 |
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| ISSN | 0022-3670 | ISBN | Medium | ||
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| Funding | Approved | $loc['no'] | |||
| Call Number | COAPS @ mfield @ | Serial | 230 | ||
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| Author | Chassignet, E.P.; Xu, X. | ||||
| Title | Impact of Horizontal Resolution (1/12° to 1/50°) on Gulf Stream Separation, Penetration, and Variability | Type | $loc['typeJournal Article'] | ||
| Year | 2017 | Publication | Journal of Physical Oceanography | Abbreviated Journal | J. Phys. Oceanogr. |
| Volume | 47 | Issue | 8 | Pages | 1999-2021 |
| Keywords | Ocean; Boundary currents; Eddies; Mesoscale processes; Ocean circulation; Ocean dynamics | ||||
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| ISSN | 0022-3670 | ISBN | Medium | ||
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| Funding | Approved | $loc['no'] | |||
| Call Number | COAPS @ mfield @ | Serial | 17 | ||
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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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| ISSN | 0022-3670 | ISBN | Medium | ||
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| Call Number | COAPS @ user @ | Serial | 951 | ||
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| Author | Zhao, X.; Zhou, C.; Zhao, W.; Tian, J.; Xu, X. | ||||
| Title | Deepwater overflow observed by three bottom-anchored moorings in the Bashi Channel | Type | $loc['typeJournal Article'] | ||
| Year | 2016 | Publication | Deep Sea Research Part I: Oceanographic Research Papers | Abbreviated Journal | Deep Sea Research Part I: Oceanographic Research Papers |
| Volume | 110 | Issue | Pages | 65-74 | |
| Keywords | Deepwater overflow; Bashi Channel; Volume transport; Spatial structure; Temporal variability | ||||
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| ISSN | 0967-0637 | ISBN | Medium | ||
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| Call Number | COAPS @ mfield @ | Serial | 92 | ||
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| Author | Roberts, M.J.; Jackson, L.C.; Roberts, C.D.; Meccia, V.; Docquier, D.; Koenigk, T.; Ortega, P.; Moreno‐ Chamarro, E.; Bellucci, A.; Coward, A.; Drijfhout, S.; Exarchou, E.; Gutjahr, O.; Hewitt, H.; Iovino, D.; Lohmann, K.; Putrasahan, D.; Schiemann, R.; Seddon, J.; Terray, L.; Xu, X.; Zhang, Q.; Chang, P.; Yeager, S.G.; Castruccio, F.S.; Zhang. C.; Wu, L. | ||||
| Title | Sensitivity of the Atlantic Meridional Overturning Circulation to Model Resolution in CMIP6 HighResMIP Simulations and Implications for Future Changes | Type | $loc['typeJournal Article'] | ||
| Year | 2020 | Publication | Journal of Advances in Modeling Earth Systems | Abbreviated Journal | J. Adv. Model. Earth Syst. |
| Volume | Issue | Pages | Accepted | ||
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| Abstract | A multi‐model, multi‐resolution ensemble using CMIP6 HighResMIP coupled experiments is used to assess the performance of key aspects of the North Atlantic circulation. The Atlantic Meridional Overturning Circulation (AMOC), and related heat transport, tends to become stronger as ocean model resolution is enhanced, better agreeing with observations at 26.5°N. However for most models the circulation remains too shallow compared to observations, and has a smaller temperature contrast between the northward and southward limbs of the AMOC. These biases cause the northward heat transport to be systematically too low for a given overturning strength. The higher resolution models also tend to have too much deep mixing in the subpolar gyre. In the period 2015‐2050 the overturning circulation tends to decline more rapidly in the higher resolution models, which is related to both the mean state and to the subpolar gyre contribution to deep water formation. The main part of the decline comes from the Florida Current component of the circulation. Such large declines in AMOC are not seen in the models with resolutions more typically used for climate studies, suggesting an enhanced risk for Northern Hemisphere climate change. However, only a small number of different ocean models are included in the study. |
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| Call Number | COAPS @ user @ | Serial | 1109 | ||
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| Author | Xu, X.; Bower, A.; Furey, H.; Chassignet, E.P. | ||||
| Title | Variability of the Iceland-Scotland Overflow Water Transport Through the Charlie-Gibbs Fracture Zone: Results From an Eddying Simulation and Observations | Type | $loc['typeJournal Article'] | ||
| Year | 2018 | Publication | Journal of Geophysical Research: Oceans | Abbreviated Journal | J. Geophys. Res. Oceans |
| Volume | Issue | 8 | Pages | ||
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| Abstract | Observations show that the westward transport of the Iceland‐Scotland overflow water (ISOW) through the Charlie‐Gibbs Fracture Zone (CGFZ) is highly variable. This study examines (a) where this variability comes from and (b) how it is related to the variability of ISOW transport at upstream locations in the Iceland Basin and other ISOW flow pathways. The analyses are based on a 35‐year 1/12° eddying Atlantic simulation that represents well the main features of the observed ISOW in the area of interest, in particular, the transport variability through the CGFZ. The results show that (a) the variability of the ISOW transport is closely correlated with that of the barotropic transports in the CGFZ associated with the meridional displacement of the North Atlantic Current front and is possibly induced by fluctuations of large‐scale zonal wind stress in the Western European Basin east of the CGFZ; (b) the variability of the ISOW transport is increased by a factor of 3 from the northern part of the Iceland Basin to the CGFZ region and transport time series at these two locations are not correlated, further suggesting that the variability at the CGFZ does not come from the upstream source; and (c) the variability of the ISOW transport at the CGFZ is strongly anticorrelated to that of the southward ISOW transport along the eastern flank of the Mid‐Atlantic Ridge, suggesting an out‐of‐phase covarying transport between these two ISOW pathways. | ||||
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| ISSN | 2169-9275 | ISBN | Medium | ||
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| Funding | Approved | $loc['no'] | |||
| Call Number | COAPS @ user @ | Serial | 1023 | ||
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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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| Call Number | COAPS @ rl18 @ | Serial | 981 | ||
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| Author | LaCasce, J.H.; Escartin, J.; Chassignet, E.P.; Xu, X. | ||||
| Title | Jet instability over smooth, corrugated and realistic bathymetry | Type | $loc['typeJournal Article'] | ||
| Year | 2018 | Publication | Journal of Physical Oceanography | Abbreviated Journal | J. Phys. Oceanogr. |
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| Abstract | The stability of a horizontally- and vertically-sheared surface jet is examined, with a focus on the vertical structure of the resultant eddies. Over a flat bottom, the instability is mixed baroclinic/barotropic, producing strong eddies at depth which are characteristically shifted downstream relative to the surface eddies. Baroclinic instability is suppressed over a large slope for retrograde jets (with a flow anti-parallel to topographic wave propagation), and to a lesser extent for prograde jets (with flow parallel to topographic wave propagation), as seen previously. In such cases, barotropic (lateral) instability dominates if the jet is sufficiently narrow. This yields surface eddies whose size is independent of the slope but proportional to the jet width. Deep eddies still form, forced by interfacial motion associated with the surface eddies, but they are weaker than under baroclinic instability and are vertically aligned with the surface eddies. A sinusoidal ridge acts similarly, suppressing baroclinic instability and favoring lateral instability in the upper layer. A ridge with a 1 km wavelength and an amplitude of roughly 10 m is sufficient to suppress baroclinic instability. Surveys of bottom roughness from bathymetry acquired with shipboard multibeam echosounding reveal that such heights are common, beneath the Kuroshio, the Antarctic Circumpolar Current and, to a lesser extent, the Gulf Stream. Consistent with this, vorticity and velocity cross sections from a 1/50° HYCOM simulation suggest that Gulf Stream eddies are vertically aligned, as in the linear stability calculations with strong topography. Thus lateral instability may be more common than previously thought, due to topography hindering vertical energy transfer. |
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| ISSN | 0022-3670 | ISBN | Medium | ||
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| Call Number | COAPS @ user @ | Serial | 998 | ||
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| Author | Zou, S.; Lozier, M.S.; Xu, X. | ||||
| Title | Latitudinal Structure of the Meridional Overturning Circulation Variability on Interannual to Decadal Time Scales in the North Atlantic Ocean | Type | $loc['typeJournal Article'] | ||
| Year | 2020 | Publication | Journal of Climate | Abbreviated Journal | J. Climate |
| Volume | 33 | Issue | 9 | Pages | 3845-3862 |
| Keywords | Deep convection; Ocean circulation; Thermocline circulation | ||||
| Abstract | The latitudinal structure of the Atlantic meridional overturning circulation (AMOC) variability in the North Atlantic is investigated using numerical results from three ocean circulation simulations over the past four to five decades. We show that AMOC variability south of the Labrador Sea (53°N) to 25°N can be decomposed into a latitudinally coherent component and a gyre-opposing component. The latitudinally coherent component contains both decadal and interannual variabilities. The coherent decadal AMOC variability originates in the subpolar region and is reflected by the zonal density gradient in that basin. It is further shown to be linked to persistent North Atlantic Oscillation (NAO) conditions in all three models. The interannual AMOC variability contained in the latitudinally coherent component is shown to be driven by westerlies in the transition region between the subpolar and the subtropical gyre (40°–50°N), through significant responses in Ekman transport. Finally, the gyre-opposing component principally varies on interannual time scales and responds to local wind variability related to the annual NAO. The contribution of these components to the total AMOC variability is latitude-dependent: 1) in the subpolar region, all models show that the latitudinally coherent component dominates AMOC variability on interannual to decadal time scales, with little contribution from the gyre-opposing component, and 2) in the subtropical region, the gyre-opposing component explains a majority of the interannual AMOC variability in two models, while in the other model, the contributions from the coherent and the gyre-opposing components are comparable. These results provide a quantitative decomposition of AMOC variability across latitudes and shed light on the linkage between different AMOC variability components and atmospheric forcing mechanisms. | ||||
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| ISSN | 0894-8755 | ISBN | Medium | ||
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| Call Number | COAPS @ user @ | Serial | 1106 | ||
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| Author | Hurlburt, HE: Metzger, EJ; Richman, JG; Chassignet, EP; Drillet, Y; Hecht, MW; Le Galloudec, O; Shriver, JF; Xu, X; Zamudio, L | ||||
| Title | Dynamical Evaluation of Ocean Models Using the Gulf Stream as an Example | Type | $loc['typeBook Chapter'] | ||
| Year | 2011 | Publication | Operational Oceanography in the 21st Century | Abbreviated Journal | |
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| Publisher | Springer | Place of Publication | Dordrecht | Editor | Schiller A., Brassington G. |
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| Call Number | COAPS @ mfield @ | Serial | 321 | ||
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