Model CCSR: Elaborations
Model CCSR is an entry in both the CMIP1 and CMIP2 intercomparisons.
The procedure for spinup/initialization to the simulation starting point
of the CCSR coupled model is as follows (reference: Masahide Kimoto, personal
First stage: The model atmosphere is integrated for 20 years starting from
the initial conditions for the AMIP experiment. The last 15 years
of this simulation is used for ocean spinup as described in the third stage
Second stage: The ocean model is integrated for 2000 years with acceleration
from static, isothermal, isohaline initial conditions. The ocean
surface conditions are restored to climatology--Levitus
(1982) SST and SSS and Hellerman
and Rosenstein (1983) wind stress.
Third stage: The ocean model is integrated for 4000 years with the atmospheric
fluxes obtained in the first-stage spinup. The ocean surface conditions
are restored to the same climatology as in the second-stage spinup, except
that the SST are modified for the last 2000 years, according to the AMIP
data. Initial flux-adjustment terms for heat and salinity are obtained.
Fourth stage: The atmosphere and ocean models are coupled, and the
system is integrated for 40 years, with the surface conditions restored
to climatology as in the third stage. Additional flux-adjustment
terms are obtained for heat and salinity.
Fifth stage: The coupled model is run for 80 years with the flux
adjustment terms for heat and salinity obtained above. The last 40
years of this run constitutes the CMIP data set.
Land Surface Processes
The skin temperature of soil and land ice is predicted by a heat diffusion
equation that is discretized in 3 layers with a zero-flux lower boundary
condition; heat capacity and conductivity are spatially uniform values.
Surface snow is treated as part of the uppermost soil layer, and thus modifies
its heat content, as well as the heat conduction to lower layers.
Soil liquid moisture is predicted in a single layer according to the "bucket"
formulation of Manabe et al. (1965)
The moisture field capacity is a spatially uniform 0.15 m, with surface
runoff occurring if the predicted soil moisture exceeds this value. Snowmelt
contributes to soil moisture, but if snow covers a grid box completely,
the permeability of the soil to falling liquid precipitation becomes
zero. For partial snow cover, the permeability decreases proportional to
increasing snow fraction.
Soil moisture is depleted by surface evaporation; the evaporation efficiency
is not determined solely by the ratio of soil moisture to its saturation
value, but is limited by the specified stomatal resistance of the vegetation.
Other effects of vegetation, such as the interception of precipitation
by the canopy and its subsequent reevaporation, are not included.
Continental runoff is returned to the oceans, by means of a river transport
model (cf. Miller et al. 1994). Runoff
instantaneously increases the river and lake mass of a grid box, which
is also affected by the local balance of precipitation and evaporation.
For each continental grid box, a river direction file indicates the downstream
routing to one of the 8 neighboring grid boxes. The river mass flux out
of a grid box is computed as a function of the river and lake mass that
lies above the local sill depth, an effective flow speed that depends on
the local orography gradient, and the mean distance to the downstream neighbor.
The flow speed is prescribed as a constant 0.3 m sec-1.
Sea ice is simulated in a single layer, with an additional layer representing
accumulated snow. Snowfall, sublimation, surface melt and bottom
melt/freeze are treated. Ice albedo is in the range 0.5-0.8 and varies
linearly according to temperature between 0 and 15 C. Thermodynamics
are modeled after Semtner (1976). Sea
ice dynamics and rheology are neglected.
Hellerman, S., and M. Rosenstein,
1983: Normal monthly wind stress over the world ocean with error estimates.
Phys. Oceanogr., 13, 1093-1104.
Levitus, S., 1982: Climatological atlas of
the world's oceans. NOAA Professional Paper 13, 173 pp.
Manabe, S., J. Smagorinsky, and R.F.
Strickler, 1965: Simulated climatology of a general circulation model with
a hydrologic cycle. Mon. Wea. Rev., 93, 769-798.
Miller, J.R., G.L. Russell, and G.
Caliri, 1994: Continental scale river flow in climate models. J. Climate,
Semtner, A.J., 1976: A model for the thermodynamic
growth of sea ice in numerical investigations of climate. J. Phys.
Oceanogr., 6, 379-389.
CMIP Documentation Directory
Last update 15 May, 2002. This page is maintained by Tom Phillips