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)