**PMIP Documentation for CCC2.0**

**Canadian Centre for Climate Modelling
and Analysis: Model CCCMA Version
2 (T32 L10) 1992**

Phone: +1-416-978-5213; Fax: +1-416-978-8905; e-mail: guido@atmosp.physics.utoronto.ca

and

Dr. McFarlane Norman A., Canadian Center for Climate Research, Atmospheric Environment Service

University of Victoria, 3964 Gordon Head Road, Victoria, BC V8W 2Y2, Canada

Phone: +1-250-363-8227; Fax: +1-250-363-8247; e-mail: Norm.McFarlane@ec.gc.ca

Number of days in each month: 31 28 31 30 31 30 31 31 30 31 30 31

The model is identical to the latest AMIP model exept for different
initial conditions and the Earth's orbital parameters.

McFarlane, N.A., Boer G.J., Blanchet J.-P., Lazare M., 1992: The Canadian Climate Centre Second-Generation General Circulation Model and Its Equiliubrium Climate, J. Climate, 5, 1013-1044. describe the features and equilibrium climate of the CCC model.

secondary refererence(s)

Some properties remain the same as those of the first-generation CCC
model documented by Boer G.J., McFarlane, N.A., Laprise R., Henderson J.D.,
Blanchet J.-P., 1984a: The Canadian Climate Centre Spectral Atmospheric
General Circulation Model, Atmos. Ocean, 22, 397-429.

dim_longitude*dim_latitude: 96*48

The model uses an eta-coordinate in the vertical with the following
levels: 0.012, 0.038, 0.088, 0.160, 0.265, 0.430, 0.633, 0.803, 0.915,
0.980

The PMIP 21fix and 21cal simulations were run on a CRAY J916 8-CPU machine.

Second-order vertical diffusion of momentum, moisture, and heat operates
above the surface. The vertically varying diffusivity depends on stability
(gradient Richardson number) and the vertical shear of the wind, following
standard mixing-length theory. Diffusivity for moisture is taken to be
the same as that for heat. Cf. McFarlane et al. (1992) for details. See
also Surface Fluxes.

Longwave radiation is modeled in six spectral intervals between wavenumbers
0 to 2.82 x 10^{5} m^{-1} after the method of Morcrette
(1984 , 1990 , 1991 ), which corrects for the temperature/pressure dependence
of longwave absorption by gases and aerosols. Longwave absorption in the
water vapor continuum follows Clough et al. (1980) . Clouds are treated
as graybodies in the longwave, with emissivity depending on optical depth
(cf. Platt and Harshvardhan 1988 ), and with longwave scattering by cloud
droplets neglected. The effects of cloud overlap in the longwave are treated
following a modified scheme of Washington and Williamson (1977) : upward/downward
irradiances are computed for clear-sky and overcast conditions, and final
irradiances are determined from a linear combination of these extreme cases
weighted by the actual partial cloudiness in each vertical layer. For purposes
of the radiation calculations, clouds occupying adjacent layers are assumed
to be fully overlapped, but to be randomly overlapped otherwise. Cf. McFarlane
et al. (1992) for further details.

For the 0fix, 0cal and 6fix Scrippstopography (Gates, W.L., and A.B. Nelson, 1975) was used.

For 21fix and 21cal the Peltier (1994) topographic differences were used :

(Peltier(21k) - Peltier(0k)) + Scrippstopogaraphy.

For 21fix, CLIMAP(21k) February and August SSTs were fit to a sinusoid to calculate mean monthly values.

For 0cal, the mixed layer model was started from modern initial conditions and run for 50 years to equilibrium.

For 21cal, the mixed layer model was started from a intial conditions
based on CLIMAP 21k reconstructed SST climatology and run for 50 years
to equilibrium.

For 21fix, CLIMAP(21k) February and August sea ice distributions were used as maxima (N.H.) and minima (N.H.), respectively, to interpolate the sea ice annual cycle.

For 21cal, CLIMAP(21k) ice distribution were allowed to evolve (receed)
to equilibrium under the influence of modern day oceanic heat transport.

Over bare dry land, the surface background albedo is determined from a weighted average for each of 24 vegetation types in the visible (0.30-0.68 micron) and near-infrared (0.68-4.0 microns) spectral bands; for wet soil, albedos are reduced up to 0.07. For vegetated surfaces, albedos are determined from a 2/3 vs 1/3 weighting of albedos of the local primary/secondary vegetation types. The local land albedo also depends on the fractional snow cover and its age (fractional coverage of a grid box is given by the ratio of the snow depth to the specified local masking depth); the resulting albedo is a linear weighted combination of snow-covered and snow-free albedos. Over the oceans, latitude-dependent albedos which range between 0.06 and 0.17 are specified independent of spectral interval. The background albedos for sea ice are 0.55 in the near-infrared and 0.75 in the visible; these values are modified by snow cover, puddling effects of melting ice (a function of mean surface temperature), and by the fraction of ice leads (a specified function of ice mass).

The longwave emissivity is prescribed as unity (i.e., blackbody emission
is assumed) for all surfaces. Cf. McFarlane et al. (1992) for further details.

The flux of surface moisture is a product of the same transfer coefficient
and stability function as for sensible heat, an evapotranspiration efficiency
(beta) factor, and the difference between the specific humidity at the
lowest atmospheric level (see Planetary Boundary Layer) and the saturation
specific humidity at the temperature/pressure of the surface. Over the
oceans and sea ice, beta is prescribed as 1; over snow, it is the lesser
of 1 or a function of the ratio of the snow mass to a critical value (10
kg/m^{2}). Over land, beta depends on spatially varying soil moisture
and field capacities (see Land Surface Processes), and on slope factors
for primary/secondary vegetation and soil types (see Surface Characteristics).
For grid boxes with fractional snow coverage, a composite beta is obtained
from a weighted linear combination of snow-free and snow-covered values.
Cf. Boer et al. (1984a) and details.

Soil moisture is predicted by a single-layer "bucket" model with field capacity and slope factors varying by primary/secondary soil and vegetation types for each grid box (see Surface Characteristics). Soil moisture budgets include both liquid and frozen water. The effective local moisture capacity is given by the product of field capacity and slope factor, with evapotranspiration efficiency beta a function of the ratio of soil moisture to the local effective moisture capacity (see Surface Fluxes). Runoff occurs implicitly if this ratio exceeds 1 (which is more likely the higher the local slope factor and the lower the local field capacity). Cf. McFarlane et al. (1992) and Boer et al. (1984a) for further details.

Last update November 9, 1998. For further information, contact: Céline Bonfils (pmipweb@lsce.ipsl.fr )