Documentation of the PMIP models (Bonfils et al. 1998)

PMIP Documentation for CLIMBER-2

CLIMate and BiosphERe groupe-Climate System Department - Potsdam Institute for Climate Impact Research : Model PIK CLIMBER-2 (7x18) 1998

PMIP Representative(s)

Andrey Ganopolski, PIK, PO BOX 60 12 03, D-14412 Potsdam, Germany, Phone : +49-331 288 2594; Fax : +49-331 288 2695; e-mail :,

Martin Claussen, PIK, PO BOX 60 12 03, D-14412 Potsdam, Germany; Phone : : +49-331 288 2522; Fax : +49-331 288 2600; e-mail :,

World Wide Web URL:

Model Designation

PIK CLIMBER-2 (7x18) 1998.

Model Identification for PMIP


PMIP run(s)

0fix, 6fix, 0cal, 21fix

Number of days in each month: 30 30 30 30 30 30 30 30 30 30 30 30

Model Lineage

Model Documentation

Petoukhov, V., A. Ganopolski, V. Brovkin, M. Claussen, A. Eliseev, C. Kubatzki, S. Rahmstorf, CLIMBER-2 : A climate model of intermediate complexity. Part I : Model description and performance for present climate, Clim. Dyn., submitted (already published as PIK-report).

Ganopolski, A. , S. Rahmstorf, V. Petoukhov, M. Claussen, 1998 : Simulation of modern and glacial climates with a coupled global model of intermediate complexity, Nature, 391, 351-356.

Numerical/Computational Properties

Horizontal Representation

Grid point.

Horizontal Resolution

Regular spherical grid, 10x51 degrees latitude-longitude.

Vertical Domain

From the surface to the top of the atmosphere.

Vertical Representation/Resolution

Different for different processes (vertically integrated thermodynamics, 10 levels dynamis, 16 levels radiative sheme).

Computer/Operating System


Computational Performance

2 model-years per minute.


Isothermal atmosphere, no snow, saturated soil.

Time Integration Scheme(s)

Explicit time scheme, one day time step for dynamics and surface processes, five days for radiative schemes.


Smoothing of some dynamical fields, correction of global averaged sea level pressure.

Sampling Frequency

One day.

Dynamical/Physical Properties

Atmospheric Dynamics

Statistical-dynamics approach. Large-scale atmospheric dynamics are described in stationary approximation. Sea level pressure is represented as a sum of zonally averaged and azonal component, computed separately. Pronostic equations for vertically integrated temperature and specific humidity.



Gravity-wave Drag


Solar Constant/Cycles

Solar constant (1 365 W/m2) and orbital parameters are calculated after PMIP recommendations. No diurnal cycle.


Radiative active gases : CO2 (200 ppm for 21 ky BP, 280 ppm for 6 ky BP), fixed ozone concentration.


Shortwave radiation is divided into two subintervals : ultraviolet + visible and near infrared. The radiative scheme accounts for water vapor, aerosols, and ozone (Feigelson et al., 1975).

Longwave radiation is based on a two-stream approximation, it accounts for water vapor and carbon dioxide. Energy fluxes are calculated using the integral transmission functions based on the Curtis-Godson approximation(Feigelson et al., 1975).

One layer effective cumulus and stratus cloudiness (randomly overlapped) with prescribed optical properties of aerosol in shortwave radiation is taken from A. A. Lacis and J. E. Hansen (1974).


Convection is treated as in Hansen et al. (1983).

Cloud Formation

One layer effective stratiform cloudiness. Cloud amount depends on relative humidity and vertical velocity at cloud base height. The height of cloud layer is a fonction of planetary boundary layer height, height of tropopause, and vertical velocity.

The fraction of cumulus cloudiness is a function of surface specific humidity, temperature, and vertical velocity.


Precipitation is function of total atmospheric water content and cloud amount.

Planetary Boundary Layer

The PBL is described using the modified Ekman formulation of Taylor which includes a spiral layer above a surface layer (Hansen et al., 1983).

Orography/Land-Sea Mask

Very schematic orography is prescribed in the model to represent Tibetan plateau and the high Antartic elevation. Fraction of ocean is prescribes for every grid cell.


For control and 6fix experiment, SST and sea-ice prescribed at the present-day climatological values. For 21cal, prescribed present-day oceani heat flux.

Sea Ice

In control and 6fix experiment, climatological sea-ice thickness and fraction are prescribed. In 21cal sea-ice thickness and fraction are calculated using a simple thermodynamic model. Surface temperature is calculated from energy balance. Effect of snow is not taken into consideration.

Snow Cover

The fraction of precipitation in the form of snow is a function of air-temperature. Fraction of snow is a function of temperature and snow thickness. Constant snow density. Influence of sublimation is neglected. Surface temperature and melting rate are defined from surface energy balance.

Surface Characteristics

Land-surface scheme is based on BATS (Dickinson et al., 1986).

Six surface types : ocean, sea-ice, trees, grass, bare soil, glaciers.

Model employs two vegetation types (trees end grass), for each grid-cell fraction of each and maximum LAI are prescribed corresponding to potential vegetation for present-day climate (Brovkin et al., 1997).

Two soil types, distinguished only in albedo.

For each surface type roughness length is prescribed (and modified in the case of snow) and albedo is calculated seperately for snow-free and snow-covered conditiond. For vegetation minimum stomatal resistance and distribution of roots is prescribed following BATS.

Surface Fluxes

Surface solar absorption is determined by surface albedos. Longwave emissivity is set to be 1.0. The surface turbulent fluxes of heat and moisture are formulated in terms of bulk formulas with stability-dependent grag/transfer coefficient. Over vegetated land, transpiration is calculated following BATS.

Land Surface Processes

Surface temperature is computed from energy balance. The heat conductivity in soil is neglected. Two-layer pronostic soil moisture model accounts for surface and sub-surface runoff and draiage . Both precipitation and snow-melt contribute to soil moisture.

Last update November 9, 1998. For further information, contact: Céline Bonfils ( )