Download - New insights from models
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New insights from models
NCAR T-shirt design, 1988
Anne Marie Treguier (LPO, Brest, France)Claus Böning (IFM Kiel, Germany)
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Models yesterday...1988: WOCE Community Model Experiment (Bryan et al)- North Atlantic, 1/3°- 220x242x30 grid points.
… and todayPOP 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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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
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Discoveries: North Brazil Undercurrent
The NBUC in the CME model (Schott and Böning, 1991).
The NBUC with ADCP data (Stramma, Fisher, Reppin 1995)
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Discovery of the North Queensland current
R.D. Hughes, D. Webb
NQc
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The Zapiola Anticyclone in the Argentine Basin : An circulation driven by eddy-topography interactions
Marvor and Alace floats (Ollitrault, Davis...)
Bottom Topography
Mean circulation, 350 mSPEM 1/3° model, coordinate
(de Miranda et al., 1999)
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3 models, same behavior3 models, same behavior
MICOM
ORCA
OCCAM
Inverse model Inverse model
AAIW
SAMW
Tasman leakage: a new route in the global conveyor belt
(Speich et al, 2002)
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Plan
1 - Knowledge of the ocean circulation
Discover and quantify Model/observations synergy
Understand processes Sensitivity studies
2 - Mechanisms of heat transport variability
Seasonal to interannual time scales
Decadal scales
What about eddies?
3 - Perspectives
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The dynamical origin of the Azores current
Azores current Strait of
Gibraltar
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The med outflow and the Azores
current
With representation of med outflow: strong AZc
Without representation of med outflow: weak AzcOzgökmen et al, 2001: MICOM 1/12° model
Jia, 1999: DYNAMO intercomparison project.
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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).
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A possible dynamical origin of the zonal flows: wind forcing
Nakano and Suginohara, 2002
Zonal flow at 140°W in a 1° model of the Pacific
(bottom: contour interval 0.1 cm/s)
Zonal flow in a shallow water model (20 modes) forced by a zonal wind
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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
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Zonal jets in the subtropical North Atlantic
Mean zonal velocity (color)
and mean velocity vectors
at 1400m depth in 3 models
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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
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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
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Heat transport and overturning
Robust relationship at 25°N
CMIP2
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Vertical overturning and horizontal gyres
Total heat transport overturning
gyre
POP 1/10° North Atlantic model (Smith et al, 2000)
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Ekman transport drives the seasonal variability in the Atlantic
Böning and Hermann, 1994Seasonal cycle at 25N:
0.2Pw = 3Sv Also at 6-8 days period:
2.5 Pw, 25 Sv
Robustness: DYNAMO models Böning et al, 2001
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Seasonal variability of heat transport in the world ocean
Jayne and Marotzke (2001)
Total heat transport
Ekman contribution
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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
Strong negative correlation between Ekman velocity and SST
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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.
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Full forcing ---- NAO-related forcing
NAO forcing of the meridional overturning
Time series of meridional heat transport at 48°N Eden and Willebrand,2002
Long time series of overturning at 48°N Eden and Jung,2002
heat flux only ---- all surface fluxes
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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
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Eddies in the meridional heat transport
30°S: 20-25% 45°N: 20-25%Tropics: mean/eddy compensation
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Warm water flux at 30°S
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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.
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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.
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Model development: topography, parameterizations…
More horizontal resolution
More vertical resolution
Future challenges
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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)
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Spatial resolution of models (2)
Increased spatial resolution has a strong influence on the pattern of anthropogenic CO2 uptake in the North Atlantic subpolar gyre
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
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Models and climate change
Bi et al, GRL, 2002: increase of the ACC transport in a transient warming scenario
Banks and Woods, 2001: Possible use of SAMW variability to detect climate change
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What resolution in the oceanto model and predict
anthropogenic climate change?