Climate Models –Part II · Climate Models –Part II GEO 458, Spring 2010 Feb 9, 2010. ... Types...
Transcript of Climate Models –Part II · Climate Models –Part II GEO 458, Spring 2010 Feb 9, 2010. ... Types...
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Climate Models – Part II
GEO 458, Spring 2010Feb 9, 2010
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Why do we need climate models?
� to gain physical insight into the behavior of the climate system.
� to get a complete spatial and temporal description of the climate.
� to predict future climate.
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Simple Energy Balance Model:
No Atmosphere case: T = 255 K ----> Too coldAtmosphere case: T = 288 K ----> Greenhouse Effect!
Atmosphere opaque to outgoing (terrestrial) longwave radiation.
Atmosphere transparent to incoming (solar) shortwave radiation.
SWLW
Last Class
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• Energy Balance Models (EBMs): 0-D/1-D
• Radiative-Convective Models (RCs): 1-D/2-D
• Statistical Dynamical Models (SDs): 2-D
• General Circulation Models (GCMs): 3-D
Types of Climate models
These models increase,
- in complexity, from first to last,
- in the degree to which they simulate particular processes, and
- in their temporal and spatial resolution.
The simplest models permit little interaction between the primary processes, radiation, dynamics and surface processes, whereas the most complex models are fully interactive.
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0-D
1-D
Energy Balance Models (EBMs)
- simulate the global radiation balance and the latitudinal energy transfer.
- Radiation Balance
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Radiative - Convective Models (RCs)
- simulate in detail the transfer of energy through depth of the atmosphere.
- Radiation Balance- Vertically Resolved Atmosphere
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Statistical Dynamical Models (SDs)
- combine the horizontal energy transfer modeled by EBMs with the
radiative-convective approach of RCs.
- Radiation Balance- Vertically Resolved Atmosphere- Surface Processes and dynamics
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General Circulation Models
The most ‘complete’ models constructed by discretizing and then solving equations which represent the basic laws governing the behavior of the atmosphere, ocean and land surface.
- Radiation Balance- Vertically Resolved Atmosphere- Surface Processes and dynamics- 3-D
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Radiative - The way in which the input and absorption of solar radiation and the
emission of infrared radiation are handled.
Dynamic - The movement of energy around the globe (from low to high latitudes) and
vertical movements (convection).
Components of Climate Model
Three major sets of processes that must be considered when constructing a climate model:
Surface processes - Inclusion of
land/ocean/ice and the resultant change in albedo, emissivity, and surface-atmosphere exchanges.
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GCMs Grid
Horizontal Resolution:~100 to 200 km
A complete spatial description of the climate.
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� Conservation of energy
� Conservation of momentum
� Conservation of mass
� Equation of state
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Parameterization
The method of incorporating a process by representing it as a simplified function of some other fully resolved variables.
• Sub-grid scale (small to be resolved in time and space) processes cannot be modeled, but must be parameterized.
• e.g. cloud formation, soil moisture transfer or oceanic eddies.
• Use of observed data as the basis of relationships.
• Time scale determines types of parameterizations needed (long term climate vs. weather prediction).
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Physical Equations and Grid
Physical Equations
Parameterizations of Processes
FeedbacksSolved for each grid cell
3-D Grid
State of climateas a function
of time
� Conservation of energy
� Conservation of momentum
� Conservation of mass
� Equation of state
� External - solar, orbital.
� Internal - volcanic eruptions, ice-sheet changes, human-induced changes.
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• BMRC: Bureau of Meteorology Research Center (Australia)• COLA: Center for Ocean-Land Atmosphere Studies (USA)• ECMWF: European Center for Medium Range Weather Forecasts• GFDL: Geophysical Fluid Dynamics Laboratory (USA)• GISS: Goddard Institute for Space Studies (USA)• GLA: Goddard Laboratory for Atmospheres (USA)• LLNL: Lawrence Livermore National Laboratories (USA)• MPI: Max Planck Institut (Germany)• MRI: Meteorological Research Institute (Japan)• NCAR: National Center for Atmospheric Research (USA)• NMC: National Meteorological Center (USA)• NTU: National Taiwan University• UKMO: United Kingdom Meteorological Office• UCLA: University of California Los Angeles
Climate Modeling Groups
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The development of climate models
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The development of climate models
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Atmospheric GCMs (AGCMs)
consist of a three-dimensional representation of the atmosphere coupled to the land surface and cryosphere. AGCMs are useful for studying atmospheric processes, the variability of climate and its response to changes in sea-surface temperature.
• Dynamics
• General circulation (winds)
• Physics
• Radiation
• Clouds
• Thermodynamics
• Moisture
• Surface and oceans
• effects of ice, snow, vegetation on temperature, albedo, emissivity, roughness
• Chemisty
• composition of the atmosphere
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Oceanic GCM
� The thermodynamic sea-ice model is an integral part of the OGCM in some cases.
� Initial condition given to the oceanic GCMs are surface temperature, sea-ice extent, surface albedo over ice-covered and ice-free regions, sea-surface salinity, partial pressure of CO2, wind stress at surface and fluxes at surface etc.
� The topography of oceanic basins is very important for getting the coastal circulation properly.
Initial Conditions for Atmospheric/Oceanic GCMs
Atmospheric GCM
� Land surface models are treated as integral components of the atmospheric model.
� Initial condition given to drive the atmospheric GCMs are winds, temperature profile, specific humidity, orography, radiativefluxes at surface and top of the atmosphere, land-sea mask, hydrological parameters, albedo, snow-ice extent etc.
� Surface boundary forcing given to the atmospheric models are through SST.
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Equilibration Time of the Climate System
Equilibration Time is the response time (or relaxation time) of the components of the climate system.
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Coupled Ocean Atmosphere Models (AOGCMs)
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• Comparison with observations/measurements.
• Comparison with paleoclimate data.
• Comparison with regional patterns of change (“finge r-printing”).
Model Validation
how well it simulates reality…
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TemperatureValidation
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Precipitation ValidationPrecipitation Validation
Simulated
Observed
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IPCC Special Report on Emissions Scenarios
Scenarios based on:
- Population- Economic growth- Technological Innovations- Energy use and sources of
energy generation
40 scenarios, all equally valid.
Future global emissions of GHG will depend on a variety of assumptions regarding human behavior and activities
A1B
A1T
A1FI
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Emission ScenariosEmission Scenarios
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Projected Surface WarmingProjected Surface Warming
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Projections of Surface TemperaturesProjections of Surface Temperatures
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Projected Patterns of Precipitation ChangesProjected Patterns of Precipitation Changes