Model CERFACS1: Elaborations
Model CERFACS1 is an entry in the CMIP1 intercomparison only.
The procedure for spinup/initialization to the simulation starting point
of the CERFACS coupled model is as follows (reference: Guilyardi
and Madec 1997):
The initial state of the atmospheric model is specified from January 1
of the tenth year of a simulation made with AMIP-prescribed SSTs and sea
Spinup of the ocean begins from a state corresponding to Levitus climatological
January. The integration proceeds for 10 years with an interior relaxation
to Levitus (1982) monthly-mean temperatures
and seasonal-mean salinities; the relaxation time scale is 50 days for
the upper 800 m and 1 year for the deep ocean. The ocean model is
forced by monthly-varying climatological wind stress after Hellerman and
Rosenstein (1983), and heat and fresh water fluxes after Esbensen
and Kushnir (1981) and Oberhuber (1988),
plus a 12-day relaxation towards surface time-varying temperature and salinity
data of Levitus. (After this dynamic spinup, the ocean model's thermodynamic
structure remains close to that of Levitus).
The atmosphere and ocean models then are coupled, and the integration proceeds
for another 50 years. (Questions regarding the coupling strategy,
such as the SST/flux-exchange frequency, the influence of the initial state,
and the need for conservation constraints in interpolating methods are
still under investigation.)
Land Surface Processes
Land surface processes are simulated by the Interactions between Soil-Biosphere-Atmosphere
(ISBA) scheme of Noilhan and Planton
(1989) as implemented in the ARPEGE model by Mahfouf
et al. (1995).
The ISBA scheme includes 5 prognostic variables: surface temperature, mean
surface temperature, surface volumetric water content, mean volumetric
water content, and the water amount intercepted by the vegetation canopy.
The time dependence of the prognostic variables are formulated as force-restore
equations after Deardorff (1977,1978). The
mean surface temperature is restored toward a climatological deep temperature
that is updated with a time constant of 20 days.
ISBA also requires 7 parameters that are prescribed or derived from other
surface characteristics: the vegetation cover, leaf area index (LAI), minimum
stomatal resistance, surface shortwave albedo, longwave emissivity, active
soil depth, and surface roughness length. In addition, climatoligical/equilibrium
temperatures and volumetric water contents, the maximum moisture capacity
of the vegetation canopy, as well as transfer coefficients and restoring
time constants are specified in the prognostic equations.
The turbulent flux of moisture from the surface to the atmosphere includes
direct evaporation from the vegetation canopy and from bare soil, as well
as transpiration by the foliage.
Transpiration ceases when the soil moisture reaches a specified wilting
point corresponding to a water potential of -15 bar; evaporation occurs
at the potential rate when soil moisture is intermediate between its field
capacity (corresponding to a hydraulic conductivity of 1x10^-4 m/day) and
a saturation value that depends on the soil texture. Surface runoff occurs
when the saturation value of soil moisture is exceeded.
Sea ice is diagnostically determined as a function of sea surface temperature
(SST) (cf. Guilyardi and Madec 1997).
If the SST becomes less than the freezing temperature for salt water, ice
forms, a constant heat flux is applied to the ocean (-2Wm-2
in the Arctic and –4Wm-2 in the Antarctic), and the atmospheric
model computes the net surface heat flux. Sea ice dynamics and rheology
Deardorff, J.W., 1977: A parameterization
of ground-surface moisture content for use in atmospheric prediction models.
J. Appl. Meteor., 16, 1182-1185.
Deardorff, J.W., 1978: Efficient prediction
of ground surface temperature and moisture, with inclusion of a layer of
vegetation. J. Geophys. Res., 83, 1889-1903.
Esbensen, S.K., and V. Kushnir,
1981: The heat budget of the global ocean: An atlas based on estimates
from marine surface observations. Climatic Research Institute, Report No.
29, Oregon State University, Corvallis, OR.
Guilyardi, E., and G. Madec,
1997: Climatology of the OPA-ARPEGE intermediate resolution coupled ocean-atmosphere
model, Climate Dyn., 13, 149-165.
Levitus, S., 1982: Climatological atlas of
the world's oceans. NOAA Professional Paper 13, 173 pp.
Mahfouf, J.-F., A.O. Manzi, J. Noilhan,
H. Giordani, and M. Deque, 1995: The land surface scheme ISBA within the
Meteo-France Climate Model ARPEGE. Part 1: Implementation and preliminary
results. J. Climate, 8, 2039-2057.
Noilhan, J., and S. Planton,
1989: A simple parameterization of land surface processes for meteorological
models. Mon. Wea. Rev., 117, 536-549.
Oberhuber, J.M., 1988: An atlas based on
the COADS data set: The budget of heat, buoyancy and turbulent kinetic
energy at the surface of the global ocean. Max-Planck-Institut fuer Meteorologie,
Report 15, Hamburg, Germany.
CMIP Documentation Directory
Last update 15 May, 2002. This page is maintained by Tom Phillips