GISS GCM Model II
The Goddard Institute for Space Studies General Circulation Model II, described fully by Hansen et al. (1983), is a three-dimensional global climate model that numerically solves the physical conservation equations for energy, mass, momentum and moisture as well as the equation of state.
The standard version of this model has a horizontal resolution of 8° latitude by 10° longitude, nine layers in the atmosphere extending to 10 mb, and two ground hydrology layers. The model accounts for both the seasonal and diurnal solar cycles in its temperature calculations.
Cloud particles, aerosols, and radiatively important trace gases (carbon dioxide, methane, nitrous oxides, and chlorofluorcarbons) are explicitly incorporated into the radiation scheme. Large-scale and convective cloud cover are predicted, and precipitation is generated whenever supersaturated conditions occur.
Snow depth is based on a balance between snowfall, melting and sublimation. The albedo of snow is a function of both depth and age. Fresh snow has an albedo of 0.85 and ages within 50 days to a lower limit of 0.5. The sea ice parameterization is thermodynamic with no relation to wind stress or ocean currents. Below -1.6°C ice of 0.5 m thickness forms over a fractional area of the grid box and henceforth grows horizontally as needed to maintain energy balance. Surface fluxes change the ocean water and sea ice temperature in proportion to the area of a grid cell they cover. Conductive cooling occurs at the ocean/ice interface, thickening the ice if the water temperature remains at -1.6°. Sea ice melts when the ocean warms to 0°C and the SST in a grid box remains at 0°C until all ice has melted in that cell. The albedo of sea ice (snow-free) is independent of thickness and is assigned a value of 0.55 in the visible and 0.3 in the near infrared, for a spectrally weighted value of 0.45.
Vegetation in the model plays a role in determining several surface and ground hydrology characteristics. Probably the most important of these is the surface albedo, which is divided into visible and near infrared components and is seasonally adjusted based on vegetation types. Furthermore, the assigned vegetation type determines the depth to which snow reflectivity can be masked. Hydrological characteristics of the soil are also based upon the prescribed vegetation types; the water holding capacity of the model's two ground layers is determined by the vegetation type as is the ability of those layers to transfer water back to the atmosphere via transpiration. Nine different vegetation classes, developed by Matthews (1984) for the GISS GCM, represent major vegetation categories and the ecological/hydrological parameters which are calculated from the vegetation. Since the GISS GCM is a fractional grid model, more than one vegetation type can be assigned to each grid box.
Sea surface temperatures (SST) are either specified from climatological input files or may be calculated using model-derived surface energy fluxes and specified ocean heat transports. The ocean heat transports vary both seasonally and regionally, but are otherwise fixed, and do not adjust to forcing changes. This mixed-layer ocean model was developed for use with the GISS GCM and is often referred to as the "Q-flux" parameterization. Full details of the Q-flux scheme are described in Russell et al. (1985), and in appendix A of Hansen et al. (1997). In brief, the convergence (divergence) at each grid cell is calculated based on the heat storage capacity of the surface ocean and the vertical energy fluxes at the air/sea interface. The annual maximum mixed-layer depth, which varies by region and season, has a global, area-weighted value of 127 meters. Vertical fluxes are derived from specified SST control runs where the specified SSTs are from climatological observations and have geographically and seasonally changing values. In the early 1990s Russell's technique was modified slightly to use five harmonics, instead of two, in defining the seasonally-varying energy flux and upper ocean energy storage. This change improved the accuracy of the approximations in regions of seasonal sea ice formation. The technique reproduces modern ocean heat transports that are similar to those obtained by observational methods (Miller et al. 1983). By deriving vertical fluxes and upper ocean heat storage from a run with appropriate paleogeography and using SSTs based on paleotemperaure proxies, q-fluxes it provides a more self-consistent method for obtaining ocean heat transports from paleoclimate scenarios that use altered ocean basin configurations.
Present-day maintenance and some development of Model II is performed within the context of the Columbia University EdGCM project. See the links at right for source code downloads and other resources provided by that project. Historical versions of Model II (e.g., the computer code used in the 1988 simulation runs) are not currently available. Please address all inquiries about the EdGCM project and about implementing Model II on modern personal computers to Dr. Mark Chandler.
Persons interested in using the most recent version of the GISS climate model, a coupled atmosphere-ocean model, should see the ModelE homepage.
Hansen, J., G. Russell, D. Rind, P. Stone, A. Lacis, S. Lebedeff, R. Ruedy, and L. Travis 1983. Efficient three-dimensional global models for climate studies: Models I and II. M. Wea. Rev. 111, 609-662, doi:10.1175/1520-0493(1983)111<0609:ETDGMF>2.0.CO;2.
Hansen, J., A. Lacis, D. Rind, G. Russell, P. Stone, I. Fung, R. Ruedy, and J. Lerner, 1984: Climate sensitivity: Analysis of feedback mechanisms. In Climate Processes and Climate Sensitivity, AGU Geophysical Monograph 29, Maurice Ewing Vol. 5. J.E. Hansen and T. Takahashi, Eds. American Geophysical Union, pp. 130-163.
Hansen, J., I. Fung, A. Lacis, D. Rind, Lebedeff, R. Ruedy, G. Russell, and P. Stone 1988. Global climate changes as forecast by Goddard Institute for Space Studies three-dimensional model. J. Geophys. Res. 93, 9341-9364.
Hansen, J., Mki. Sato, R. Ruedy, A. Lacis, K. Asamoah, K. Beckford, S. Borenstein, E. Brown, B. Cairns, B. Carlson, B. Curran, S. de Castro, L. Druyan, P. Etwarrow, T. Ferede, M. Fox, D. Gaffen, J. Glascoe, H. Gordon, S. Hollandsworth, X. Jiang, C. Johnson, N. Lawrence, J. Lean, J. Lerner, K. Lo, J. Logan, A. Luckett, M.P. McCormick, R. McPeters, R.L. Miller, P. Minnis, I. Ramberran, G. Russell, P. Russell, P. Stone, I. Tegen, S. Thomas, L. Thomason, A. Thompson, J. Wilder, R. Willson, and J. Zawodny 1997. Forcings and chaos in interannual to decadal climate change. J. Geophys. Res. 102, 25679-25720, doi:10.1029/97JD01495.
Matthews, E. 1984. Prescription of Land-Surface Boundary Conditions in GISS GCM II: A Simple Method Based on High-Resolution Vegetation Data Bases. NASA TM-86096. National Aeronautics and Space Administration. Washington, D.C.
Miller, J.R., G.L. Russell, and L.-C. Tsang 1983. Annual oceanic heat transports computed from an atmospheric model. Dynam. Atmos. Oceans 7, 95-109.
Russell, G.L., J.R. Miller, and L.-C. Tsang 1985. Seasonal oceanic heat transports computed from an atmospheric model. Dynam. Atmos. Oceans 9, 253-271.
Downloads & Links
Model II Source Code
The 8°×10° (lat×lon) version of the GISS Model II is still in use as a research tool for paleoclimate and planetary studies, for very long simulations, or where limited computing resources are available.
An up-to-date copy of this slightly modified version, with minor updates and bugfixes, is available from the EdGCM project.
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The Columbia University EdGCM software is a graphical user interface which simplifies set-up and control of GISS Model II. This educational suite gives users the ability to create and conduct "Rediscovery Experiments", simulations that reproduce many of the hundreds of experiments that have been conducted and published using this version of the NASA GISS GCM.
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