research insights from the serious games institute: new models for applied research?
New insights from models
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Transcript of New insights from models
New insights from models
NCAR T-shirt design, 1988
Anne Marie Treguier (LPO, Brest, France)Claus Böning (IFM Kiel, Germany)
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
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
Discoveries: North Brazil Undercurrent
The NBUC in the CME model (Schott and Böning, 1991).
The NBUC with ADCP data (Stramma, Fisher, Reppin 1995)
Discovery of the North Queensland current
R.D. Hughes, D. Webb
NQc
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)
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)
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
The dynamical origin of the Azores current
Azores current Strait of
Gibraltar
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.
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).
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
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
Zonal jets in the subtropical North Atlantic
Mean zonal velocity (color)
and mean velocity vectors
at 1400m depth in 3 models
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
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
Heat transport and overturning
Robust relationship at 25°N
CMIP2
Vertical overturning and horizontal gyres
Total heat transport overturning
gyre
POP 1/10° North Atlantic model (Smith et al, 2000)
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
Seasonal variability of heat transport in the world ocean
Jayne and Marotzke (2001)
Total heat transport
Ekman contribution
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
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.
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
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
Eddies in the meridional heat transport
30°S: 20-25% 45°N: 20-25%Tropics: mean/eddy compensation
Warm water flux at 30°S
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.
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.
Model development: topography, parameterizations…
More horizontal resolution
More vertical resolution
Future challenges
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)
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
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
What resolution in the oceanto model and predict
anthropogenic climate change?