Coupled general circulation modeling
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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.
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.
- 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).