1. Mixed Layer Ocean Model: Model Physics and Climate
CAM(2+) Coupled to a
Mixed Layer Ocean Model:
Model Physics and Climate
Christophe Cassou
Mike Alexander
Clara Deser
CCSM Workshop Santa Fe 2004

2. Coupling between CAM (2+) - ocean Mixed Layer Model (MLM)
What is the COUP_MLM option?
1.1 Introduction : the model
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
DTm = Qnet/rcH
Qcor
+Qcor/rcH
Mixed Layer Model
Tm/Sm
Qnet
Qcor
Tb/Sb
Varying H
Accounts for vertical processes

3. An individual column model with a uniform mixed layer
MLM in more detail
1.2 Introduction : the model
An individual column model with a uniform mixed layer
atop 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

4. Kinetic energy equation)
Mixed layer Temperature change in MLM
1.3 Introduction: the model
Qwe
Vertical
Entrainment
(We from turbulent
Kinetic energy equation)
Qswh
Solar
Penetration
Qnet
Qcor
Diffusion CA
Convective
Adjustment h
(MLD)
Tm1
Tb1

5. Below ice there is fresh water flux due to: - ice volume change
The salinity equation
1.4 Introduction: the model
Below ice there is fresh water flux due to:
- ice volume change
- brine ejection
weighted by the ice fraction

6. SST bias tied to ice (ovals)
SST biais
2.1 Validation of the climatology
Departure between 80yr mean
and observed (HADISST) climatology
January
Max : +0.8
Max : +1
Max : +1.2
SST too warm in summer
due to over-estimated shoaling
SST bias tied to ice (ovals)
ice melts early Labrador Sea
Ice melt late north of Russia
July

7. Overestimation over theTrade winds domain and no diurnal cycle
Mixed Layer Depth
2.2 Validation of the climatology
80y mean MLD for January-February-March average
Underestimates
of the MLD
Correct representation
Over the main atm.
Baroclinic zone
Overestimation over theTrade winds
domain and no diurnal cycle

8. Model (80y mean) Observations March September Realistic SI Extent
Ice concentration (Northern Hemisphere)
2.3 Validation of the climatology
Model
(80y mean)
March
September
Observations
Realistic SI Extent
but UNrealistic
SI Thickness

9. Model (80y mean) Observations March September
Ice concentration (Southern Hemisphere)
2.4 Validation of the climatology
Model
(80y mean)
March
September
Observations

10. PC1 (bars)/5yr-running mean (green line)
Variability in the Indian Ocean and its links to the atmosphere
3.1 Variability
EOF1 for DJF SST(contour) /Regressed precipitation (filled)
Regressed MSLP
PC1 (bars)/5yr-running mean (green line)

11. SVD between SST No significant auto-corr. for MSLP (white noise) +
Variability in the North Pacific
3.2 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
Reddening of the SST
spectrum

12. SVD between SST No significant auto-corr. for MSLP (white noise) +
Variability in the North Atlantic
3.3 Variability
SVD between SST
(color) and MSLP
(contour) FMA season
Years
SST
MSLP
No significant auto-corr.
for MSLP (white noise) +
Quasi-biennal dominant
peak
Reddening of the SST
spectrum

13. EOF1 for DJF MSLP(contour) Regressed SST(filled)
The North Atlantic Osciallation
3.4 Variability
EOF1 for DJF MSLP(contour)
Regressed SST(filled)
White spectrum with a strong
quasi-biennal peak
Strongly linked to the
Artic Oscillation
Regressed ice frac
More Ice
Less Ice
Regressed Mixed Layer Depth
Deeper
Shallower

14. From March (0) May (+2) Oct (+7) +0.5 Jan (+10) +0.6 60 30
Persistence of SST anomalies : Monthly Autocorrelation
3.5 Variability
From March (0) 60 30
May (+2)
Oct (+7)
+0.5
Jan (+10)
+0.6

15. 3D SVD between JAS Ocean Temperature
Relationship between the deep ocean and the surface atmosphere
3.6 Variability
3D SVD between JAS Ocean Temperature
[30m-400m] and previous FMA
MSLP (contour)

16. From March (0) May (+2) +0.5 +0.6 Oct (+7) Jan (+10) 60 30
The Reemergence mechanism
3.7 Variability
From March (0) 60
Reemergence mechanism 30
May (+2)
+0.5
+0.6
Oct (+7)
Jan (+10)

17. 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 project (See J. Hansen, MIT)