1) CGCMs are coupled general circulation models that combine atmospheric and oceanic GCMs to allow the lower boundary conditions of the atmosphere to be determined interactively by ocean processes. 2) CGCM3.1 is a third generation CGCM developed by CCCMA that runs at T47 and T63 resolutions with ocean grids of roughly 1.4x0.9 degrees and 1.85 degrees respectively. 3) A study assessed CGCM3.1's wind fields in the Persian Gulf, finding it generally underestimated wind speeds compared to ECMWF reanalysis data.

2. Coupled General
Circulation Modeling

3. General Circulation Models
Newton's Laws of Motion
1st Law of Thermodynamics
Conservation of Mass and Moisture
Hydrostatic Balance
Ideal Gas Law

4. Spectrum of Climate Models
Energy Balance Models (EBM’s)
Atmospheric General Circulation Models (AGCM)
AGCM + Slab Ocean Model
Coupled Ocean Atmosphere GCM (OAGCM)
EMIC
ESM

5. Physical basis of climate models:
• The atmosphere is a fluid on a rotating planet:
• Drag at the surface and within the atmosphere affects the momentum budget
• Water vapour evaporates from the surface, condenses to form clouds and heats the
atmosphere when it is lost through precipitation
• Heating from solar radiation and cooling from thermal radiation
• Models therefore need to include equations for;
• 3 components of wind (or vorticity & divergence), including Coriolis and drag
• equation of state and conservation of water
• thermodynamics, including heating by condensation and radiation

6. Continue:
• The ocean is also a fluid, but incompressible. It is heated by solar
radiation and cooled by evaporation and thermal emission from the
surface. No internal heating, but salinity strongly affects the density
and hence the circulation
• Additional models have been developed to include the land surface,
cryosphere, atmospheric chemistry and aerosols, carbon cycle etc
• Processes that are sub-grid in scale are modelled by parametrizations

7. Is There a Better Set of Lower
Boundary Conditions?
• Yes! The lower boundary conditions for the atmosphere could be
determined interactively in response to processes internal to the
model.
• This goal can be achieved by coupling the atmosphere to an ocean
model.

8. What is CGCM?
• It is Coupled General Circulation Model
• Atmospheric (AGCMs) and oceanic GCMs (OGCMs) can be coupled to
form an atmosphere-ocean coupled general circulation model (CGCM
or AOGCM).

9. CGCM-3 and CGCM 3.1
• These are the third generation Coupled Global Climate Model.
• Developed by Canadian Centre for Climate Modelling and Analysis
(CCCma). The initial version of CGCM3 was developed and ran on a
NEC SX/6 vector supercomputer and CGCM 3.1 was run on a new
distributed memory IBM computer system.

10. Continue:
• The third version of the Canadian Centre for Climate Modelling
and Analysis(CCCma) Coupled Global Climate Model (CGCM3) makes use of
the same ocean component as that used in the earlier,
The Second Generation Coupled Global Climate Model, but it makes use of
the substantially updated atmospheric component.

11. Features of CGCM 3.1:
• CGCM3.1 is run at two different resolutions
1. The T47 version has a surface grid whose spatial
resolotion is roughly 3.75 degrees lat/lon and 31 levels in the
vertical.
2. The ocean grid shares the same land mask as the
atmsosphere, but has four ocean grid cells underlying every
atmospheric grid cell. The ocean resolution in this case is
roughly 1.85 degrees, with 29 levels in the vertical.

12. Continue
• The T63 version has a surface grid whose spatial resolution is roughly
2.8 degrees lat/lon and 31 levels in the vertical.
• As before the ocean grid shares the same land mask as the
atmosphere, but in this case there are 6 ocean grids underlying every
atmospheric grid cell.
• The ocean resolution is therefore approximately 1.4 degrees in
longitude and 0.94 degrees in latitude.
• This provides slightly better resolution of zonal currents in the Tropics,
more nearly isotropic resolution at mid latitudes, and somewhat
reduced probles with converging meridians in the Arctic.

13. Continue:
Model Sponsor
Atmosphere
Top Resolutio
n
Ocean
Resolution
Sea Ice
Coupling /
Adjustments
Land Surface
CGCM3.1
(T47)
CCCMA
Top = 1 hPa
T47 (1.9°x1.
9°)
L31
0.9 x 1.4°
L29
Rheology,
leads
Heat, fresh
water
Layers,
canopy,
routing

14. CGCM 3 features:
Agency
Canadian Centre for Climate Modelling and Analysis
(CCCma)
Model name Coupled Global Climate Model (CGCM3)
Atmospheric prognostic variables See model documentation
Oceanic prognostic variables See model documentation
Atmospheric resolution T63, L31
Oceanic resolution roughly 1.4 Lon x 0.9 Lat, L29

15. Assessment of CGCM 3.1 wind field in
the Persian Gulf : (research paper)
• Increasing of the greenhouse gases emission causes the
climate changes. Therefore, usage of the marine renewable
energy resources such as wind and wave energies has been
increased during the last decades. Climate variability can
change the wind and consequently wave patterns and the
available energy amounts. Therefore, assessment of the
potential effect of climate change on the wind regime is
important

16. • In this paper, wind characteristics obtained from a global
climate model (CGCM 3.1) is used for assessing the effects of
climate change on the wind regime in the Persian Gulf. CGCM
3.1 results were compared quantitatively with those of ECMWF
in the Persian Gulf and the results showed that in comparison to
ECMWF, CGCM 3.1 wind speeds are mostly underestimated for
both average and maximum values

17. Atmosphere-Swamp Ocean:
• Ocean is represented as a wet surface with zero heat capacity.
• Surface temperature is interactively determined.
• Albedo of swamp surface increases when temperature falls
below freezing.

18. EMICs:
• EMICs: Earth System Models of Intermediate Complexity
• Designed to contain many feedbacks of full AOGCM but
consume far less computer time.
• Used for climate simulations that require long time scales (i.e.,
>1000 years).