Model COLA 2: Elaborations
Model COLA2 is an entry in the CMIP1 intercomparison only.
The procedure for spinup/initialization of the COLA coupled model was a
follows (reference: E. Schneider, personal communication):
- The model atmosphere was integrated to equilibrium using as a
conditions either prescribed SSTs or the forcing provided by coupling
a mixed-layer ocean model.
- The model ocean was initialized, whole-volume, to the
- The models then were coupled and integrated without flux
190 years. The first 80 years of the run were discarded, and
variables were computed from the last 100 years.
Land Surface Processes
- 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,
from dry leaves includes detailed modeling of stomatal and canopy
direct evaporation from the wet canopy and from bare soil is also
Precipitation interception by the canopy is simulated, and its
into the ground is limited to less than the hydraulic conductivity of
- Soil temperature is determined in two layers by the force-restore
of Deardorff (1978). Soil moisture,
is predicted from diffusion equations in three layers, is increased by
infiltrated precipitation and snowmelt, and is depleted by
direct evaporation, and drainage. Both surface runoff and deep runoff
gravitational drainage are simulated, but the contribution of runoff to
the freshwater flux into the ocean model is not included.
- The sea ice parameterization (cf. the appendix to Schneider
and Zhu 1998) is a simple prognostic single-layer thermodynamic
Given surface fluxes provided by the atmospheric model, the scheme
changes in ice thickness and surface temperature, and the modified
of heat and fresh water supplied to the underlying ocean. The time step
is semi-analytic to maintain stability.
- Sea ice forms over the whole of an ocean grid box when the
of the topmost ocean layer is predicted to fall below the saltwater
temperature. Melting occurs at the top or bottom of the ice
if the respective temperatures of these surfaces are predicted to be
this freezing point. Freshwater fluxes from the atmosphere are
by the sea ice, but freezing or melting at the ice bottom causes
changes in the freshwater flux to the ocean.
- The ice albedo is a constant, independent of surface temperature
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
assumed to be linear, and the temperature at the bottom surface is
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
exchanged between the ice and the topmost ocean layer, consistent with
freezing/melting, to keep the ocean surface temperature at the
- Sea ice dynamics and rheology are not represented.
Chief Differences from the
In addition to differences in horizontal resolution, the atmospheric
of the COLA 2 model differs from AMIP model COLA
COLA1.1 (R40 L18) 1993 in the following respects:
The relaxed Arakawa-Schubert scheme of Moorthi
and Suarez (1992) replaces the modified Kuo convective
that is used in the AMIP
A cloud scheme similar to that of the NCAR CCM3
(cf. Kiehl et al. 1996)
replaces the Slingo
scheme that is used in the AMIP
Bryan, K., and L. Lewis, 1979: A
mass model of the world ocean. J. Geophys. Res., 84,
Deardorff, J.W., 1978: Efficient
of ground surface temperature and moisture, with inclusion of a layer
vegetation. J. Geophys. Res., 83, 1889-1903.
Kiehl, J.T., G.B. Bonan, B.A.
B.P. Briegleb, D.L. Williamson, and P.J. Rasch, 1996: Description of
NCAR Community Climate Model (CCM3). NCAR Tech. Note,
152 pp. [Available from National Center for Atmospheric Research,
Levitus, S., 1982: Climatological atlas
the world's oceans. NOAA Professional Paper 13, 173 pp.
Moorthi, S., and M.J. Suarez,
1992: Relaxed Arakawa-Schubert: A parameterization of moist convection
for general circulation models. Mon. Wea. Rev., 120,
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,
Sensitivity of the simulated annual cycle of sea surface temperature in
the equatorial Pacific to sunlight penetration. J. Climate, 11,
Sellers, P.J., Y. Mintz, Y.C. Sud,
and A. Dalcher, 1986: A simple biosphere model (SiB) for use within
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
studies. J. Climate, 4, 345-364.
CMIP Documentation Directory
Last update 15 May, 2002. For questions or comments, contact
Tom Phillips (firstname.lastname@example.org).