Model COLA 1: Elaborations
Participation
Model COLA1 is an entry in the CMIP1 intercomparison only.
Spinup/Initialization
The procedure for spinup/initialization of the COLA coupled model was a
follows (reference: E. Schneider, personal communication):
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The model atmosphere was integrated to equilibrium using as a boundary
conditions either prescribed SSTs or the forcing provided by coupling to
a mixed-layer ocean model.
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The model ocean was initialized, whole-volume, to the observations (e.g.,
Levitus
1982 data).
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The models then were coupled and integrated without flux adjustments. The
first 3 years of the coupled run were discarded to eliminate evidence of
coupling shock, and the next 50 years also were discarded, when running
at low resolution, to eliminate slow drift.
Land Surface Processes
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Land surface processes are simulated following the Xue
et al. (1991) modification of the SiB model of Sellers
et al. (1986). Within the single-story vegetation canopy, evapotranspiration
from dry leaves includes detailed modeling of stomatal and canopy resistances;
direct evaporation from the wet canopy and from bare soil is also treated.
Precipitation interception by the canopy is simulated, and its infiltration
into the ground is limited to less than the hydraulic conductivity of the
soil.
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Soil temperature is determined in two layers by the force-restore method
of Deardorff (1978). Soil moisture, which
is predicted from diffusion equations in three layers, is increased by
infiltrated precipitation and snowmelt, and is depleted by evapotranspiration,
direct evaporation, and drainage. Both surface runoff and deep runoff from
gravitational drainage are simulated, but the contribution of runoff to
the freshwater flux into the ocean model is not included.
Sea Ice
-
The sea ice parameterization (cf. the appendix to Schneider
and Zhu 1998) is a simple prognostic single-layer thermodynamic model.
Given surface fluxes provided by the atmospheric model, the scheme calculates
changes in ice thickness and surface temperature, and the modified fluxes
of heat and fresh water supplied to the underlying ocean. The time step
is semi-analytic to maintain stability.
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Sea ice forms over the whole of an ocean grid box when the temperature
of the topmost ocean layer is predicted to fall below the saltwater freezing
temperature. Melting occurs at the top or bottom of the ice
if the respective temperatures of these surfaces are predicted to be above
this freezing point. Freshwater fluxes from the atmosphere are unmodified
by the sea ice, but freezing or melting at the ice bottom causes appropriate
changes in the freshwater flux to the ocean.
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The ice albedo is a constant, independent of surface temperature or ice
melt. Solar radiation does not penetrate the ice and there are no
other internal heat sources. Overlying snow cover also does not affect
the ice thermodynamics. The temperature gradient within the ice is
assumed to be linear, and the temperature at the bottom surface is prescribed
to be the saltwater freezing point. The heat flux into the ocean
is determined by conduction down the ice temperature gradient, which is
controlled by the ice thickness and the top surface temperature. Heat is
exchanged between the ice and the topmost ocean layer, consistent with
freezing/melting, to keep the ocean surface temperature at the saltwater
freezing point.
-
Sea ice dynamics and rheology are not represented.
References
Bryan, K., and L. Lewis, 1979: A water
mass model of the world ocean. J. Geophys. Res., 84, 2503-2517.
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.
Levitus, S., 1982: Climatological atlas of
the world's oceans. NOAA Professional Paper 13, 173 pp.
Schneider, E.K., Z. Zhu, B.S. Giese,
B. Huang, B.P. Kirtman, J. Shukla, and J.A. Carton, 1997: Annual cycle
and ENSO in a coupled ocean-atmosphere general circulation model. Mon.
Wea. Rev., 125, 680-702.
Schneider, E. K., and Z. Zhu, 1998:
Sensitivity of the simulated annual cycle of sea surface temperature in
the equatorial Pacific to sunlight penetration. J. Climate, 11,
1932-1950.
Sellers, P.J., Y. Mintz, Y.C. Sud,
and A. Dalcher, 1986: A simple biosphere model (SiB) for use within general
circulation models. J. Atmos. Sci., 43, 505-531.
Xue, Y.-K., P.J. Sellers, J.L. Kinter
II, and J. Shukla, 1991: A simplified biosphere model for global climate
studies. J. Climate, 4, 345-364.
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Last update 15 May, 2002. This page is maintained by Tom Phillips
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