19_ClimateModels

19_ClimateModels - ESM 203: General Circulation Models...

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1 ESM 203: General Circulation Models (Climate System Models) Jeff Dozier &Tom Dunne Fall 2007
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2 General Circulation Models ~ 2 dozen in world ---- all major nations figure that they’d better develop their own technology so they don’t have to trust other nations in negotiations about blame and trade-offs. National Center for Atmospheric Research, Boulder Geophysical Fluid Dynamics Lab, Princeton NASA Goddard Institute for Space Studies, NYC Canadian Hadley Centre (UK) Max Planck Inst. (Germany) Japan Different methods, so in detail they predict markedly different regional patterns of change (say, 3-6 ° C different in regional predictions of average winter temperature under doubled carbon dioxide). But all predict global averages of ~2-5 ° C with polar areas warming more than equator (upto ~10 ° C ).
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3 Elements of a climate system model (1) Atmosphere model Radiation and energy balance (Earth and Sun) Interactions between different levels in the atmosphere Surface effects (albedo) Clouds, water vapor, CO 2 and other gases, aerosols Computationally intensive Atmospheric dynamics Winds, pressure distribution, boundary-layer processes Hydrologic cycle Evaporation and precipitation Precipitation formation (least reliable part of forecasts)
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4 Elements of a climate system model (2) Land surface model Soil moisture storage and release Vegetation roles Snow and ice Ocean model Dynamics, deep water formation, boundary processes Fine resolution and long integrations, so computationally intensive Ice sheet model Sea ice model “Primitive”
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5 General Circulation Models GCMs more general than ‘climate models’ because they contain the behavior of the ocean circulation, terrestrial hydrology, and sea ice. Ice sheet energetics included, but not dynamics ---leading to underestimation of response to warming Earliest models didn’t allow ocean to circulate. Yet ocean is largest store of heat on planet, so subtle changes in its turnover of heat and carbon dioxide have a big effect on calculated temperatures of atmosphere.
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6 Conceptual Design of a GCM A. Henderson-Sellers and K. McGuffie, A Climate Modelling Primer, Wiley, 1987
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7 Strategy of climate model operation Begin by specifying atmospheric conditions at a large number of grid points on surface and at a number of elevations above it Specify boundary conditions everywhere on the lower boundary of the atmosphere: land/ocean/ice; temperature; veg. cover; etc. Specify the forcing mechanisms you are trying to model the consequences of : Milankovitch variations; CO 2 levels; land use; volcanic dust or aerosol inputs, etc. Solve the equations describing conservation of energy (First Law of Thermo), conservation of momentum (Newton’s Second Law), conservation of mass, and the gas laws to predict the changes that will result from the given fields of atmospheric characteristics, given the boundary conditions and external forcings
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This note was uploaded on 08/06/2008 for the course ESM 203 taught by Professor Dozier,dunne during the Fall '07 term at UCSB.

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19_ClimateModels - ESM 203: General Circulation Models...

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