Model Information of Potential Use to the IPCC Lead Authors and the AR4.

 

GISS-AOM

 

16 February 2005

 

 

I. Model Identity:

   A. Institution: NASA Goddard Institute for Space Studies (NASA/GISS),

                   USA

   B. Model name: AOM 4x3

   C. Vintage: AOM 5x4 was first published in 1995;

               AOM 4x3 was completed in 2004

   D. References: Web site for AOM 4x3: http:/aom.giss.nasa.gov

                  Refereed publication of AOM 5x4 formulation:

                  Russell GL, Miller JR, Rind D, 1995.  A coupled

                  atmosphere-ocean model for transient climate change

                  studies.  Atmosphere-Ocean 33 (4), 683-730.

   E. Model performance: of AOM 5x4:

                         Lucarini L, Russell GL, 2002.  Comparison of

                         mean climate trends in the northern hemisphere

                         between National Centers for Environmental

                         Prediction and two atmosphere-ocean model

                         forced runs.  JGR, 107 (D15),

                         10.1029/2001JD001247

   F. Climate sensitivity: Early version of AOM 5x4 was estimated to

                           have dTeq = 2.65 (C) for doubling CO2 by

                           diagnosing ocean heat intake;

                           AOM 4x3 has not been examined

   G. Contacts: For all pieces: Gary L. Russell,

                Gary.L.Russell@nasa.gov

 

II. What can be included (interactively) and was it active in the model

    version that produced output stored in the PCMDI database?

    A. Atmospheric chemistry: no

    B. Interactive biogeochemistry: no

    C. Aerosols: Boucher's monthly-decade sulfate burden (mg/m^2)

                 (downloaded from PCMDI web site) was converted to an

                 optical depth by global coefficient [.030 (m^2/mg)]

                 and treated as tropospheric sulfate aerosols with

                 particular vertical distribution;

                 indirect effects were not separately modeled

    D. Dynamic vegetation: no

    E. Ice sheets: nothing other than that covered under IV. D. 9.

 

III. Projects: AMIP: 5x4 atmospheric model between AOM 5x4 and AOM 4x3

               CMIP: early version of AOM 5x4, should be discarded

 

IV. Component model characteristics (of current IPCC model version):

    A. Atmosphere

       1. Resolution: 4 degrees longitude, 3 degrees latitude, 12

                      vertical layers, heat and water vapor have mean

                      value and three prognostic directional gradients

                      inside each cell

       2. Numerical scheme: grid point model;

                            forward step, linear upstream shceme used

                            for linear advection (heat and water vapor);

                            leap frog, second order center-difference

                            C-grid scheme for non-linear advection

                            (momentum);

                            combination of fixed mass and sigma

                            coordinate vertical layering;

                            4 layers above 204 hPa on average;

                            2 layers below 875 hPa on average;

       3. Prognostic variables: all are three dimensional;

                                MA = mass (kg/m^2)

                                UA = eastward velocity (m/s) on C-grid

                                VA = northward velocity (m/s) on C-grid

                                H0M = mean potential enthalpy (J)

                                HXM, HYM, HZM = eastward, northward

                                  and vertical gradients of potential

                                  enthalpy (J)

                                Q0M = mean water vapor (kg)

                                QXM, QYM, QZM = eastward, northward

                                  and vertical gradients of water

                                  vapor (kg)

       4. Parameterizations: AOM web site:

             http://aom.giss.nasa.gov/DOC4X3/ATMOC4X3.TXT

          a. Clouds: see AOM web site

          b. Convection: see AOM web site

          c. Boundary layer: see AOM web site

          d. Radiation: see AOM web site;

                        Lacis AA, Oinas V, 1991.  A description of the

                        correlated k distributed method for modeling

                        nongray gaseous absorption, thermal emission,

                        and multiple scattering in vertically

                        inhomogeneous atmospheres.  JGR, 96, 9027-9063.

          e. Drag at model top: a drag proportional to the square of

                                wind is applied to top layer velocity

                                components

 

    B. Ocean

       1. Resolution: 4 degrees longitude, 3 degrees latitude, up to 16

                      vertical layers, heat and salt have mean value

                      and three prognostic directional gradients inside

                      each cell

       2. Numerical scheme: grid point model;

                            forward step, linear upstream shceme used

                            for linear advection (heat and salt);

                            leap frog, second order center-difference

                            C-grid scheme for non-linear advection

                            (momentum);

                            sigma coordinate vertical layering but

                            variable number of layers (consequently

                            each layer has approximately the same mass

                            per unit area in all cells);

                            free surface;

                            Bousinesq approximation not used;

                            freshwater fluxes change ocean mass

       3. Prognostic variables: all are three dimensional;

                                MO = mass (kg/m^2)

                                UO = eastward velocity (m/s) on C-grid

                                VO = northward velocity (m/s) on C-grid

                                G0M = mean potential enthalpy (J)

                                GXM, GYM, GZM = eastward, northward

                                  and vertical gradients of potential

                                  enthalpy (J)

                                S0M = mean salt (kg)

                                SXM, SYM, SZM = eastward, northward and

                                  vertical gradients of salt (kg)

       4. Parameterizations: AOM web site:

             http://aom.giss.nasa.gov/DOC4X3/ATMOC4X3.TXT

          a. Eddy parameterization: none

          b. Bottom boundary: bottom drag, see AOM web site

          c. Mixed-layer: KPP vertical mixing scheme;

                          Large WG, McWilliams JC, Doney SC, 1994.

                          Oceanic vertical mixing: review and a model

                          with non-local boundary layer

                          parameterization.  Rev. Geophys., 32, 363-403.

          d. Sunlight: penetrates into top 3 layers (about 51 meters);

                       Paulson CA, Simpson JJ, 1977.  Irradiance

                       measurements in the upper ocean.  J. Appl.

                       Oceanogr., 7, 952-956.

          e. Tidal mixing: none

          f. River flow: enters into top ocean layer affecting mass,

                         mean heat, and horizontal gradients of heat

                         and salt

          g. Isolated seas: subresolution straits connect isolated

                            seas to main ocean (Mediterranean Sea,

                            Baltic Sea, Black Sea, Red Sea, White Sea,

                            Persian Gulf), see AOM web site

          h. North pole: treated same as in atmosphere, single vector

                         velocity at pole (which appears to rotate);

                         mass, heat and salt have same value at all

                         polar longitudes, GXM=GYM=SXM=SYM=0;

 

    C. Sea Ice

       1. Resolution: same as ocean (4x3), 2 mass layers, 4 thermal

                      layers, single ice thickness

       2. Numerical scheme: velocity components defined on C-grid;

                            advection of ice use modified linear

                            upstream scheme;

                            call once each hour with other source terms

       3. Prognostic variables: RSI = horizontal sea ice cover

                                RSIX,RSIY = eastward and northward

                                  gradients of horizontal sea ice cover

                                MSI(2) = snow and sea ice mass (kg/m^2)

                                HSI(4) = heat content of layer (J/m^2)

                                PSI = internal sea ice pressure

                                USI = eastward velocity (m/s) on C-grid

                                VSI = northward velocity (m/s) on C-grid

       4. Completeness: sea ice velocity accelerated by seven terms:

                        atmospheric stress, ocean drag, Coriolis and

                        metric term, surface pressure and ocean tilt,

                        internal sea ice pressure, parallel sea ice

                        stresses, island and coastline blocking factor;

                        minimum open ocean is 6% / [ice thickness (m)];

                        snow thicker than 91.66 (kg/m^2) is compacted

                        into ice

       5. Salinity: none

       6. Brine rejection: all salt drops into ocean when ice forms

       7. North pole: velocity not defined nor used;

                      RSI,MSI,HSI,PSI have same value at all polar

                      longitudes, RSIX=RSIY=0

 

    D. Continents: each 4x3 cell is either all ocean or all continent

       1. Resolution: fixed fractions of continental cell are

                      ground, land ice, or lake,

                      ground can be partially covered by snow,

                      lake can be partially covered by lake ice;

                      ground has 4 layers plus fith layer for snow,

                      ground layer thicknesses: .0625, .25, 1, 4 (m);

                      land ice has 4 layers;

                      liquid lake has 2 layers,

                      lake ice is treated like sea ice

       2. Frozen soil: each ground layer has water mass and heat

                       content which determines frozen fraction

       3. Rivers: excess precipitation and snow melt (surface runoff)

                  is fed into lake in same cell;

                  underground runoff depends on soil types and

                  standard deviation of topography;

                  hand made river direction file:

                  http://aom.giss.nasa.gov/rdv4x3.html

       4. Snow on ground: precipitation is uniform over a grid cell;

                          snow on snow-free ground adds to snow-covered

                          ground at rate of 21 (kg/m^2);

                          when snow on snow-covered ground exceeds 42

                          (kg/m^2) it spreads covering snow-free ground;

                          rain compacts some snow into ice;

                          if snow melts below 20 (kg/m^2), snow-covered

                          ground is reduced horizontally

       5. Water storage: each 4 layers of ground cells have fractions

                         of soil types: sand, silt, clay, peat, rock;

                         hydraulic diffusivity depends on soil types

                         and liquid water availability;

                         water flux depends on hydraulic diffusivity,

                         liquid water, and air space;

                         evaporation from root layers 2, 3 and 4 during

                         growing season when sun is up, only from layer

                         1 othertimes

       6. Albedo: determined by visible and near infrared separately;

                  integrated snow albedo ranges from .50 to .85

                  depending on thickness and age;

                  integrated ice albedo is .45;

                  integrated ground albedo depends on vegetation and

                  season and ranges from .50 for bright desert to .11

                  for rain forest

       7. Vegetation: fixed fractions for 10 different types of ground

                      cells;

                      affects surface albedo, surface roughness,

                      evpaoration, hydraulic and thermal diffusivities,

                      and underground runoff

       8. Prognostic variables: see

            http:/aom.giss.nasa.gov/CODE4X3/C477C.S

       9. Ice sheets: ice in layers 1 and 2 is 182, 3 is 910, 4 is 6370

                      (kg/m^2) [sums to about 8.3 (m)];

                      snow is distributed uniformly over land ice cell;

                      snow exceeding 91.66 (kg/m^2) is compacted into

                      ice, equal amount of ice is removed from layer 4,

                      and ice is then relayered;

                      surface melt water can refreeze in any of 4

                      layers, after that it seeps out into ocean via

                      river direction file

 

    E. Coupling details:

       1. Frequency: atmosphere and subsurface reservoirs exchange

                     fluxes once each hour

       2. Conservation: water mass and static energy are conserved

                        exactly;

                        surface momentum stresses are conserved between

                        atmosphere and ocean

       3. Fluxes:

          a: atmo-ocean: PREC = precipitation (kg/m^2)

                         EPRE = energy of precipitation (J/m^2)

                         SRHDT = solar radiation absorbed (J/m^2)

                         TRHDT = thermal radiation emitted (J/m^2)

                         DMUA = eastward momentum stress (kg/m*s)

                         DMVA = northward momentum stress (kg/m*s)

                         W0 = dew minus evaporation (kg/m^2)

                         E0 = turbulent plus radiation fluxes (J/m^2)

          b: atmo-land: PREC = precipitation (kg/m^2)

                        EPRE = energy of precipitation (J/m^2)

                        SRHDT = solar radiation absorbed (J/m^2)

                        TRHDT = thermal radiation emitted (J/m^2)

                        W0 = dew minus evaporation (kg/m^2)

                        E0 = turbulent plus radiation fluxes (J/m^2)

                        WR = evaporation from roots (kg/m^2)

          c: land-ocean: MFLUX = mass flux from rivers (kg)

                         EFLUX = energy flux from rivers (J)

                         BERGM = ice bergs from Antarctica (kg)

                         BERGE = energy of ice bergs from Antarctica (J)

          d: sea ice-ocean: DMOO = ice formed on open ocean (kg/m^2)

                            DEOO = energy of ice formation on open ocean

                            DMOI = ice formed beneath old ice (kg/m^2)

                            DEOI = energy of ice formation beneath ice

                            RUNS = melted surface ice (kg/m^2)

                            ENRG = heat from ocean to melt sea ice

                            DMO  = ice melted at bottom of ice

                            DRSI = ice melted horizontally

                            DMUI = eastward momentum stress (kg/m*s)

                            DMVI = northward momentum stress (kg/m*s)

                            E1 = conductive energy flux (J/m^2)

          e: atmo-sea ice: PREC = precipitation (kg/m^2)

                           EPRE = energy of precipitation (J/m^2)

                           SRHDT = solar radiation absorbed (J/m^2)

                           TRHDT = thermal radiation emitted (J/m^2)

                           DMUA = eastward momentum stress (kg/m*s)

                           DMVA = northward momentum stress (kg/m*s)

                           W0 = dew minus evaporation (kg/m^2)

                           E0 = turbulent plus radiation fluxes (J/m^2)

          f: land ice-sea ice: DRSI = increase in horizontal sea ice

                                      cover from Antarctic ice calving

                               HGIT = energy from Antarctic ice calving

       4. Flux adjustments: no

 

V. Simulation Details

 

         A. PIcntrl: 1850 to 2100

   C480: B. 200-year spinup from Levitus climatological conditions

   C490: B. 250-year spinup from Levitus climatological conditions

         C. Monthly varying, but annually fixed, some industrial and

            natural aerosols and Boucher's 1850 sulfate burden, see

            solar constant is fixed at 1367 (W/m^2)

 

         A. 20C3M: 1850 to 2000

   C483: B. 200-year spinup from Levitus climatological conditions

   C493: B. 250-year spinup from Levitus climatological conditions

         D. Greenhouse gases: http://aom.giss.nasa.gov/IN/GHGA1B.LP ;

            Boucher's time varying sulfate burden (1850 to 2000), see

            http://aom.giss.nasa.gov/cp4x3in.html (#16);

            other forcing agents have monthly changes, but no annual

            changes

 

         A. SRES B1: 2000 to 2100

   C484: B. Initialized from end of C483

   C494: B. Initialized from end of C493

         D. Greenhouse gases: http://aom.giss.nasa.gov/IN/GHGB1.LP ;

            Boucher's time varying sulfate burden (2000 to 2100) for

            IPCC SRES B1, see

            http://aom.giss.nasa.gov/cp4x3in.html (#16);

            other forcing agents have monthly changes, but no annual

            changes

 

         A. SRES A1B: 2000 to 2100

   C485: B. Initialized from end of C483

   C495: B. Initialized from end of C493

         D. Greenhouse gases: http://aom.giss.nasa.gov/IN/GHGA1B.LP ;

            Boucher's time varying sulfate burden (2000 to 2100) for

            IPCC SRES A1B, see

            http://aom.giss.nasa.gov/cp4x3in.html (#16);

            other forcing agents have monthly changes, but no annual

            changes