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New insights from models

New insights from models. Anne Marie Treguier (LPO, Brest, France) Claus Böning (IFM Kiel, Germany). NCAR T-shirt design, 1988. … and today. POP global 1/10° model (Maltrud and McClean) 3600x2400x40 grid points. OCCAM global 1/12° model (Coward and Webb) 4320x1735x66 grid points.

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New insights from models

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  1. New insights from models Anne Marie Treguier (LPO, Brest, France) Claus Böning (IFM Kiel, Germany) NCAR T-shirt design, 1988

  2. … and today POP global 1/10° model (Maltrud and McClean) 3600x2400x40 grid points. OCCAM global 1/12° model (Coward and Webb) 4320x1735x66 grid points Models yesterday... 1988: WOCE Community Model Experiment (Bryan et al) - North Atlantic, 1/3° - 220x242x30 grid points.

  3. Plan 1 - Knowledge of the ocean circulation Discover and quantify Models/observations synergy Understand processes Sensitivity studies 2 - Mechanisms of heat transport variability Seasonal to interannual time scales: wind forcing Decadal scales : buoyancy fluxes come into play What about eddies? 3 - Perspectives

  4. Discoveries: North Brazil Undercurrent The NBUC in the CME model (Schott and Böning, 1991). The NBUC with ADCP data (Stramma, Fisher, Reppin 1995)

  5. Discovery of the North Queensland current R.D. Hughes, D. Webb NQc

  6. Mean circulation, 350 m SPEM 1/3° model,  coordinate (de Miranda et al., 1999) Marvor and Alace floats (Ollitrault, Davis...) The Zapiola Anticyclone in the Argentine Basin : An circulation driven by eddy-topography interactions Bottom Topography

  7. AAIW SAMW Tasman leakage: a new route in the global conveyor belt 3 models, same behavior (Speich et al, 2002) MICOM Inverse model ORCA OCCAM

  8. Plan 1 - Knowledge of the ocean circulation Discover and quantifyModel/observations synergy Understand processesSensitivity studies 2 - Mechanisms of heat transport variability Seasonal to interannual time scales Decadal scales What about eddies? 3 - Perspectives

  9. The dynamical origin of the Azores current Azores current Strait of Gibraltar

  10. The med outflow and the Azores current Jia, 1999: DYNAMO intercomparison project. With representation of med outflow: strong AZc Without representation of med outflow: weak Azc Ozgökmen et al, 2001: MICOM 1/12° model

  11. Zonal current in the Brazil basin Float displacements: Hogg and Owens, 1999 1/6° CLIPPER Atlantic model, Treguier et al. 0.28° global POP model Maltrud et al. Displacements over 2 years at 2400m (North Atlantic Deep Water).

  12. A possible dynamical origin of the zonal flows: wind forcing Nakano and Suginohara, 2002 Zonal flow in a shallow water model (20 modes) forced by a zonal wind Zonal flow at 140°W in a 1° model of the Pacific (bottom: contour interval 0.1 cm/s)

  13. Dependency on model resolution Zonal velocity (mean over 10 years) at 2000m (westward in green. Contour interval 0.4 cm/s) 1° model 1/6° model

  14. Zonal jets in the subtropical North Atlantic Mean zonal velocity (color) and mean velocity vectors at 1400m depth in 3 models

  15. High resolution models improve our knowledge of the ocean circulation - Models begin to look like reality - High resolution basin scale models can be used to run sensitivity studies - Many key processes affecting the large scale circulation have very small scale

  16. Plan 1 - Knowledge of the ocean circulation Discoveries and quantification Understanding processes 2 - Mechanisms of heat transport variability Seasonal to interannual time scales Decadal scales What about eddies? 3 - Perspectives

  17. CMIP2 Heat transport and overturning Robust relationship at 25°N

  18. Vertical overturning and horizontal gyres POP 1/10° North Atlantic model (Smith et al, 2000) Total heat transport overturning gyre

  19. Robustness: DYNAMO models Böning et al, 2001 Ekman transport drives the seasonal variability in the Atlantic Böning and Hermann, 1994 Seasonal cycle at 25N: 0.2Pw = 3Sv Also at 6-8 days period: 2.5 Pw, 25 Sv

  20. Seasonal variability of heat transport in the world ocean Jayne and Marotzke (2001) Total heat transport Ekman contribution

  21. Strong negative correlation between Ekman velocity and SST Ekman transport and SAMW variability Rintoul and England, 2002 Variability of temperature and salinity at 45°S, 145°E (winter mixed layer) in a coupled model

  22. Interannual variability of the meridional overturning at 45°N in the Atlantic Beismann et al, 2002 Amplitude: 3 Sv Robustness across models Link with the wind stress field.

  23. Long time series of overturning at 48°N Eden and Jung,2002 Full forcing ---- NAO-related forcing heat flux only ---- all surface fluxes NAO forcing of the meridional overturning Time series of meridional heat transport at 48°N Eden and Willebrand,2002

  24. Plan 1 - Knowledge of the ocean circulation Discover and quantify Understand processes 2 - Mechanisms of heat transport variability Seasonal to interannual time scales Decadal scales What about eddies? 3 - Perspectives

  25. Eddies in the meridional heat transport 45°N: 20-25% 30°S: 20-25% Tropics: mean/eddy compensation

  26. Warm water flux at 30°S

  27. Eddy contribution at 30°S - The « classical » eddy flux v’h’ or v’T’:  20-25% of total  no parameterization - Even when the « classical » eddy flux is zero, translating eddies have an effect : modification of mean flow properties.

  28. Oceanic heat transport variability: model insights - Models reveal the importance of wind-forced variability: Ekman transport on seasonal scales Robustness at interannual scales - On decadal time scales, more complex processes importance of buoyancy fluxes - Even with models, the effect of eddies is difficult to quantify.

  29. Future challenges • Model development: topography, parameterizations… • More horizontal resolution • More vertical resolution

  30. Spatial resolution of models (1) Modelling the western boundary currents and deep reciculations. 1/6° model recirculation cell: 2Sv Currentmeter data: a recirculation of more than 20Sv? (Weatherly et al, 2000)

  31. Spatial resolution of models (2) Anthropogenic CO2 flux in the subpolar North Atlantic (december 1989, in mol/m²/year). Arne Biastoch, 2002. 4/3° (100 km) FLAME model 1/3° (20 km) FLAME model Increased spatial resolution has a strong influence on the pattern of anthropogenic CO2 uptake in the North Atlantic subpolar gyre

  32. Banks and Woods, 2001: Possible use of SAMW variability to detect climate change Models and climate change Bi et al, GRL, 2002: increase of the ACC transport in a transient warming scenario

  33. What resolution in the oceanto model and predict anthropogenic climate change?

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