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Author (up) Ajayi, A.; Le Sommer, J.; Chassignet, E.; Molines, J.-M.; Xu, X.; Albert, A.; Cosme, E. url  doi
openurl 
  Title Spatial and Temporal Variability of the North Atlantic Eddy Field From Two Kilometric-Resolution Ocean Models Type $loc['typeJournal Article']
  Year 2020 Publication Journal of Geophysical Research: Oceans Abbreviated Journal J. Geophys. Res. Oceans  
  Volume 125 Issue 5 Pages  
  Keywords submesoscales; fine‐ scales; enstrophy; eddies; SWOT  
  Abstract Ocean circulation is dominated by turbulent geostrophic eddy fields with typical scales ranging from 10 to 300 km. At mesoscales (>50 km), the size of eddy structures varies regionally following the Rossby radius of deformation. The variability of the scale of smaller eddies is not well known due to the limitations in existing numerical simulations and satellite capability. Nevertheless, it is well established that oceanic flows (<50 km) generally exhibit strong seasonality. In this study, we present a basin&#8208;scale analysis of coherent structures down to 10&#8201;km in the North Atlantic Ocean using two submesoscale&#8208;permitting ocean models, a NEMO&#8208;based North Atlantic simulation with a horizontal resolution of 1/60 (NATL60) and an HYCOM&#8208;based Atlantic simulation with a horizontal resolution of 1/50 (HYCOM50). We investigate the spatial and temporal variability of the scale of eddy structures with a particular focus on eddies with scales of 10 to 100&#8201;km, and examine the impact of the seasonality of submesoscale energy on the seasonality and distribution of coherent structures in the North Atlantic. Our results show an overall good agreement between the two models in terms of surface wave number spectra and seasonal variability. The key findings of the paper are that (i) the mean size of ocean eddies show strong seasonality; (ii) this seasonality is associated with an increased population of submesoscale eddies (10&#65533;50&#8201;km) in winter; and (iii) the net release of available potential energy associated with mixed layer instability is responsible for the emergence of the increased population of submesoscale eddies in wintertime.  
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  Corporate Author Thesis  
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  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 2169-9275 ISBN Medium  
  Area Expedition Conference  
  Funding Approved $loc['no']  
  Call Number COAPS @ user @ Serial 1104  
Permanent link to this record
 

 
Author (up) Chassignet, E.P.; Xu, X. url  doi
openurl 
  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  
  Abstract  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  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 17  
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Author (up) LaCasce, J.H.; Escartin, J.; Chassignet, E.P.; Xu, X. url  doi
openurl 
  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.  
  Volume Issue Pages  
  Keywords  
  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.
 
  Address  
  Corporate Author Thesis  
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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 @ user @ Serial 998  
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Author (up) Legg, S.; Briegleb, B.; Chang, Y.; Chassignet, E.P.; Danabasoglu, G.; Ezer, T.; Gordon, A.L.; Griffies, S.; Hallberg, R.; Jackson, L.; Large, W.; Özgökmen, T.M.; Peters, H.; Price, J.; Riemenschneider, U.; Wu, W.; Xu, X.; Yang, J. url  doi
openurl 
  Title Improving Oceanic Overflow Representation in Climate Models: The Gravity Current Entrainment Climate Process Team Type $loc['typeJournal Article']
  Year 2009 Publication Bulletin of the American Meteorological Society Abbreviated Journal Bull. Amer. Meteor. Soc.  
  Volume 90 Issue 5 Pages 657-670  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0003-0007 ISBN Medium  
  Area Expedition Conference  
  Funding Approved $loc['no']  
  Call Number COAPS @ mfield @ Serial 683  
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Author (up) Maloney, E.D.; Gettelman, A.; Ming, Y.; Neelin, J.D.; Barrie, D.; Mariotti, A.; Chen, C.-C.; Coleman, D.R.B.; Kuo, Y.-H.; Singh, B.; Annamalai, H.; Berg, A.; Booth, J.F.; Camargo, S.J.; Dai, A.; Gonzalez, A.; Hafner, J.; Jiang, X.; Jing, X.; Kim, D.; Kumar, A.; Moon, Y.; Naud, C.M.; Sobel, A.H.; Suzuki, K.; Wang, F.; Wang, J.; Wing, A.A.; Xu, X.; Zhao, M. url  doi
openurl 
  Title Process-Oriented Evaluation of Climate and Weather Forecasting Models Type $loc['typeJournal Article']
  Year 2019 Publication Bulletin of the American Meteorological Society Abbreviated Journal Bull. Amer. Meteor. Soc.  
  Volume 100 Issue 9 Pages 1665-1686  
  Keywords  
  Abstract Realistic climate and weather prediction models are necessary to produce confidence in projections of future climate over many decades and predictions for days to seasons. These models must be physically justified and validated for multiple weather and climate processes. A key opportunity to accelerate model improvement is greater incorporation of process-oriented diagnostics (PODs) into standard packages that can be applied during the model development process, allowing the application of diagnostics to be repeatable across multiple model versions and used as a benchmark for model improvement. A POD characterizes a specific physical process or emergent behavior that is related to the ability to simulate an observed phenomenon. This paper describes the outcomes of activities by the Model Diagnostics Task Force (MDTF) under the NOAA Climate Program Office (CPO) Modeling, Analysis, Predictions and Projections (MAPP) program to promote development of PODs and their application to climate and weather prediction models. MDTF and modeling center perspectives on the need for expanded process-oriented diagnosis of models are presented. Multiple PODs developed by the MDTF are summarized, and an open-source software framework developed by the MDTF to aid application of PODs to centers' model development is presented in the context of other relevant community activities. The paper closes by discussing paths forward for the MDTF effort and for community process-oriented diagnosis.  
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  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0003-0007 ISBN Medium  
  Area Expedition Conference  
  Funding Approved $loc['no']  
  Call Number COAPS @ user @ Serial 1088  
Permanent link to this record
 

 
Author (up) Roberts, M.J.; Jackson, L.C.; Roberts, C.D.; Meccia, V.; Docquier, D.; Koenigk, T.; Ortega, P.; Moreno&#8208; 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. url  openurl
  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  
  Keywords  
  Abstract A multi&#8208;model, multi&#8208;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&#8208;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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  Series Editor Series Title Abbreviated Series Title  
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  Area Expedition Conference  
  Funding Approved $loc['no']  
  Call Number COAPS @ user @ Serial 1109  
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Author (up) Trossman, D.S.; Arbic, B.K.; Straub, D.N.; Richman, J.G.; Chassignet, E.P.; Wallcraft, A.J.; Xu, X. url  doi
openurl 
  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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  Abstract  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  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 230  
Permanent link to this record
 

 
Author (up) Xu, X.; Bower, A.; Furey, H.; Chassignet, E.P. url  doi
openurl 
  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 123 Issue 8 Pages 5808-5823  
  Keywords Iceland; Scotland overflow water; Charlie; Gibbs fracture zone; variability; volume transport; eddying simulation  
  Abstract Observations show that the westward transport of the Iceland&#8208;Scotland overflow water (ISOW) through the Charlie&#8208;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&#8208;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&#8208;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&#8208;Atlantic Ridge, suggesting an out&#8208;of&#8208;phase covarying transport between these two ISOW pathways.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 2169-9275 ISBN Medium  
  Area Expedition Conference  
  Funding Approved $loc['no']  
  Call Number COAPS @ user @ Serial 952  
Permanent link to this record
 

 
Author (up) Xu, X.; Bower, A.; Furey, H.; Chassignet, E.P. url  doi
openurl 
  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  
  Keywords  
  Abstract Observations show that the westward transport of the Iceland&#8208;Scotland overflow water (ISOW) through the Charlie&#8208;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&#8208;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&#8208;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&#8208;Atlantic Ridge, suggesting an out&#8208;of&#8208;phase covarying transport between these two ISOW pathways.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 2169-9275 ISBN Medium  
  Area Expedition Conference  
  Funding Approved $loc['no']  
  Call Number COAPS @ user @ Serial 1023  
Permanent link to this record
 

 
Author (up) Xu, X.; Chassignet, E.P., Wang, F. url  doi
openurl 
  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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  Series Volume Series Issue Edition  
  ISSN ISBN Medium  
  Area Expedition Conference  
  Funding Approved $loc['no']  
  Call Number COAPS @ rl18 @ Serial 981  
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