cam(2+) coupled to a mixed layer ocean model: model physics and climate
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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
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
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
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
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
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
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
Model(80y mean)
Observations
March September
Ice concentration (Northern Hemisphere) 2.3 Validation of the climatology
Realistic SI Extentbut UNrealisticSI Thickness
Model(80y mean)
Observations
March September
Ice concentration (Southern Hemisphere)
2.4 Validation of the climatology
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
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
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
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
From March (0)
May (+2)
60
30
Jan (+10)
+0.6
Oct (+7)
+0.5
Persistence of SST anomalies : Monthly Autocorrelation 3.5 Variability
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
From March (0)
Oct (+7) Jan (+10)
May (+2)
60
30
+0.6+0.5
Reemergence mechanism
The Reemergence mechanism 3.7 Variability
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)
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