cam(2+) coupled to a mixed layer ocean model: model physics and climate
DESCRIPTION
CAM(2+) Coupled to a Mixed Layer Ocean Model: Model Physics and Climate. Christophe Cassou Mike Alexander Clara Deser. CCSM Workshop Santa Fe 2004. In the code, COUP_MLM is equivalent to COUP_SOM, which allows for coupling with a Slab Ocean Model (SOM). Slab Ocean. Mixed Layer Model. - PowerPoint PPT PresentationTRANSCRIPT
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CAM(2+) Coupled to a
Mixed Layer Ocean Model:
Model Physics and Climate
CCSM Workshop Santa Fe 2004
Christophe CassouMike Alexander
Clara Deser
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What is the COUP_MLM option?
Coupling between CAM (2+) - ocean Mixed Layer Model (MLM) - the thermodynamic portion of the NCAR sea ice model (CSIM4)
In the code, COUP_MLM is equivalent to COUP_SOM,which allows for coupling with a Slab Ocean Model (SOM)
Slab Ocean
Tm Fixed H
Qnet
Tm = Qnet/cH
Qcor
+Qcor/cH
Mixed Layer Model
Tm/Sm
Qnet Qcor
Tb/Sb
Varying H
Accounts for vertical processes
1.1 Introduction : the model
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An individual column model with a uniform mixed layeratop a layered model that represents conditions in the pycnocline
MLM model: Alexander et al (2002, J. Clim) based on Gaspar’s (1988, JPO) formulation
Model characteristics:• Same grids as the atmosphere (128 lon x 64 lat)• 36 vertical levels (from 0m to 1500m depth) with a better resolution close to surface (10 levels for the first 50m)• Realistic bathymetry
MLM in more detail 1.2 Introduction : the model
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h (MLD)
Tb1
Tm1
Qnet Qcor
Qswh
SolarPenetration
Qwe
VerticalEntrainment
(We from turbulentKinetic energy equation)
CA
ConvectiveAdjustment
Diffusion
Mixed layer Temperature change in MLM 1.3 Introduction: the model
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Below ice there is fresh water flux due to: - ice volume change
- brine ejectionweighted by the ice fraction
The salinity equation 1.4 Introduction: the model
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Departure between 80yr mean and observed (HADISST) climatology
SST bias tied to ice (ovals)-ice melts early Labrador Sea-Ice melt late north of Russia
January
July
Max : +0.8
Max : +1
Max : +1.2
SST too warm in summerdue to over-estimated shoaling
SST biais 2.1 Validation of the climatology
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80y mean MLD for January-February-March average
Underestimatesof the MLD
Correct representationOver the main atm. Baroclinic zone
Overestimation over theTrade winds domain and no diurnal cycle
Mixed Layer Depth 2.2 Validation of the climatology
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Model(80y mean)
Observations
March September
Ice concentration (Northern Hemisphere) 2.3 Validation of the climatology
Realistic SI Extentbut UNrealisticSI Thickness
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Model(80y mean)
Observations
March September
Ice concentration (Southern Hemisphere)
2.4 Validation of the climatology
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EOF1 for DJF SST(contour) /Regressed precipitation (filled)
PC1 (bars)/5yr-running mean (green line)Regressed MSLP
Variability in the Indian Ocean and its links to the atmosphere 3.1 Variability
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SVD between SST(color) and MSLP (contour) FMA season
No significant auto-corr.for MSLP (white noise) +Quasi-biennal dominant peak
Years
SST
MSLP
MSLPSST
Reddening of the SSTspectrum
Variability in the North Pacific 3.2 Variability
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SVD between SST(color) and MSLP (contour) FMA season
Years
SST
MSLP
MSLPSST
No significant auto-corr.for MSLP (white noise) +Quasi-biennal dominant peak
Reddening of the SSTspectrum
Variability in the North Atlantic 3.3 Variability
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EOF1 for DJF MSLP(contour) Regressed SST(filled)
Regressed ice frac
More Ice Less Ice
Regressed Mixed Layer Depth
Deeper
Shallower
White spectrum with a strongquasi-biennal peakStrongly linked to the Artic Oscillation
The North Atlantic Osciallation 3.4 Variability
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From March (0)
May (+2)
60
30
Jan (+10)
+0.6
Oct (+7)
+0.5
Persistence of SST anomalies : Monthly Autocorrelation 3.5 Variability
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3D SVD between JAS Ocean Temperature[30m-400m] (color @30m) and previous FMAMSLP (contour)
Relationship between the deep ocean and the surface atmosphere 3.6 Variability
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From March (0)
Oct (+7) Jan (+10)
May (+2)
60
30
+0.6+0.5
Reemergence mechanism
The Reemergence mechanism 3.7 Variability
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Discussion
• Model has run for more than 150 years now and appears to be stable (basic climate variability structures are correctly simulated, some biais though –model and configuration)
• Originally MLM coupled to CAM2 plan is to support with newer versions of CAM (coupled with CAM3 in progress)
• Ocean can be a mix of specified SSTs and MLM (e.g. observed SSTs specified in the tropical Pacific)
• Useful for a wide variety of coupled model studies: between CAM-SOM CCSM (Reemergence experiments running right now)
• Will be used in climate@home project (See J. Hansen, MIT)