Model NCAR (CSM): Elaborations
Model NCAR (CSM) is an entry in both the CMIP1 and CMIP2
and also is supplying an optional extended set of output data in
The spinup/initialization procedure for the CMIP I
experiment was as follows (cf. Boville
and Gent 1998 and NCAR
Section 1996 for further details):
- The atmospheric model was spun up in a 10-year integration with
monthly climatological SSTs (Shea et
- The ocean model was spun up first in an uncoupled mode by
of momentum, heat, and freshwater. The momentum and turbulent heat
and the net surface longwave flux were derived by bulk formulae from
winds, air temperatures, and specific humidities obtained from the
National Center for Environmental Prediction (NCEP) reanalysis data for
1985-1988 (Kalnay et al. 1996).
longwave radiation also was derived from a bulk formula that included
addition to the surface temperatures and humidities) daily cloud
data of the International Satellite Cloud Climatology Project (ISCCP) (Rossow
and Schiffer 1991). The surface net shortwave radiation was derived
from daily ISCCP insolation data of Bishop
and Rossow (1991). The freshwater flux was derived from satellite
Sounding Unit (MSU) estimates of monthly precipitation (Spencer
1993) minus the surface evaporation obtained directly from the
latent heat flux plus a weak salinity restoring term. (Before their
to the ocean model, the net heat and freshwater fluxes were adjusted to
ensure that their global annual averages were near zero.) In addition,
in areas of sea ice, ocean temperature and salinity were strongly
to the 50-meter average climatology of Levitus
(1982). Sea ice extents were diagnostically determined from the
climatological SSTs prescribed in the atmospheric spin up.
- To reduce the coupling shock, the ocean model was spun up for
years by recycling the fluxes obtained from the 10-year atmospheric
The model atmosphere and ocean then were coupled and integrated for 300
years without application of any flux corrections.
Land surface processes are simulated by the Land Surface Model (LSM) of
(1996 , 1998). See also Web site http://www.cgd.ucar.edu/cms/lsm/
summary documentation and other information.
- The simulated thermodynamics involve lateral ice growth in leads,
ice melt, and changes of state associated with the energy balance at
top and bottom of the ice. The representation of lateral growth/melt is
after Parkinson and
(1979), while that of the vertical energy balance follows Semtner
(1976) with some modifications. The calculation of the
thermodynamic state variables is based on the diffusion of heat through
the external and internal boundaries of a three-layer system. If the
thickness is greater than 0.5 m, two layers of ice are maintained;
if present, constitutes a third layer. When the ice thickness is
between 0.25 m and 0.5 m, only a single layer is retained. If the
ice thickness falls below 0.25 m, the zero-layer model of Semtner
(1976) is employed. The entire net heat flux from the ocean is
to lateral ice growth/melt; thus, when computing the vertical energy
the heat flux at the bottom of the ice is set to zero.
- Snow accumulation on sea ice is computed from the
minus evaporation). The freshwater flux to the ocean due to ice
is parameterized by a method similar to Parkinson
(1979), with conservation of salt. Any snow melt is added to the
flux into the ocean. Precipitation on sea ice at the freshwater melting
point (0 deg C) is assumed to fall directly into the ocean.
- A fraction (0.3, assuming cloudy conditions 75 percent of the
solar radiation is allowed to penetrate snow-free ice. The penetrating
radiation may be transmitted to the ocean or absorbed in the ice,
on its thickness. The absorbed fraction contributes to the internal
of ice in brine pockets, following Semtner
(i.e., the absorbed flux is stored in a heat reservoir without
the overall ice thickness). The ice albedo depends on snow cover/depth
and surface temperature. (The albedo computation assumes a mix of
snow-covered and snow-free ice and uses a proxy ‘snow fraction’.)
The albedos of ice and snow depend on spectral interval, and on whether
these surfaces are dry or melting.
- Sea ice dynamics are based on the cavitating-fluid approximation
and Hibler (1990): ice has a finite resistance to compression, but
diverges freely without resistance to shear stress. The ice momentum
include the Coriolis force, wind stress, ocean current stress,
acceleration from the ocean surface tilt, and the gradient of
ice pressure due to compression. Ice velocity equations are
at the corner points of an Arakawa B-grid in spherical coordinates,
a modified Pollard and
advection scheme. Advected variables include ice concentration and
heat content of each ice layer, brine heat reservoir, and snow volume
heat content. For further details, cf. Bettge
et al. (1996).
Chief Differences from Closest AMIP Model
The NCAR (CSM) coupled model includes the NCAR
Climate Model Version 3 (CCM3) as its atmospheric component (see also
chief differences between CCM3 and AMIP model NCAR
CCM2 (T42 L18) 1992 include:
For further details on the NCAR (CSM) model, see Web
In CCM3, effects of trace greenhouse gases on longwave radiation
added to the radiation scheme of the AMIP
model. Cloud radiative properties also are changed. Cf. Kiehl
et al. (1998a, b) for
Bettge, T.W., J.W. Weatherly, W.M.
D. Pollard, B.P Briegleb, and W.G. Strand, 1996: The NCAR CSM Sea Ice
NCAR Tech. Note NCAR/TN-425+STR, 25 pp.
Bishop, J.K.B., and W.B.
1991: Spatial and temporal variability of global surface solar
Geophys. Res., 96, 16,839-16,858.
Bonan, G.B., 1996: A Land
Model (LSM Version 1.0) for Ecological, Hydrological, and Atmospheric
Technical Description and User's Guide. NCAR Technical Note
National Center for Atmospheric Research, Boulder, Colorado, 150 pp.
Bonan, G.B., 1998: The land
climatology of the NCAR land surface model (LSM 1.0) coupled to the
Community Climate Model (CCM3). J. Climate, 11,
P.R. Gent, 1998: The NCAR Climate System Model, Version One. J.
Flato, G.M., and W.D. Hibler,
On a simple sea-ice dynamics model for climate studies. Ann.
Hack, J. J.,
A.A.M. Holtslag, 1998: Climate simulation sensitivity to a revised
boundary layer parameterization. In preparation.
Hack, J.J., J.T.
and J. Hurrell, 1998: The hydrologic and thermodynamic structure of the
NCAR CCM3. J. Climate, 11, 1179-1206.
Kalnay, E.C., M. Kanamitsu, R.
W. Collins, D. Deaven, L. Gandin, M. Iredell, S. Saha, G. White, J.
Y. Zhu, M. Chelliah, W. Ebisuzaki, W. Higgins, J. Janowiak, K.C. Mo, C.
Ropelewski, A. Leetmaa, R. Reynolds, and R. Jenne, 1996: The NCEP/NCAR
reanalysis project. Bull. Am Meteor. Soc., 77, 437-471.
Kiehl, J.T., J.J. Hack, G. Bonan,
Boville, D. Williamson, and P. Rasch, 1998a: The National Center for
Research Community Climate Model: CCM3. J. Climate,
Kiehl, J.T., J.J. Hack, and J.
1998b: The energy budget of the NCAR Community Climate Model: CCM3. J.
Climate, 11, 1151-1178.
Levitus, S., 1982: Climatological atlas
the world's oceans. NOAA Professional Paper 13, 173 pp.
(NCAR OS), 1996: The NCAR CSM ocean model. NCAR Technical Note
National Center for Atmospheric Research, Boulder, Colorado.
Parkinson, C.L. and W.M.
Washington, 1979: A large-scale numerical model of sea ice. J. Geophys.
Res., 84, 311-337.
Pollard, D., and S.L.
1994: Sea-ice dynamics and CO2 sensitivity in a global climate model.
Rossow,W.B., and R.A.
1991: ISCCP cloud data products. Bull. Am. Meteor. Soc., 72,
Semtner, A.J., 1976: A model for the
growth of sea ice in numerical investigations of climate. J.
Oceanogr., 6, 379-389.
Shea, D.J., K.E. Trenberth, and R.W.
Reynolds, 1990: A global monthly sea surface temperature climatology.
Technical Note NCAR/TN-345, 167 pp.
Spencer, R.W., 1993: Global oceanic
from the MSU during 1979-91 and comparisons to other climatologies. J.
Climate, 6, 13021-1326.
Washington, W.M., and G.A.
1996: High-latitude climate change in a global coupled
ice model with increased atmospheric CO2. J. Geophys. Res.,
Zhang, G.J., and N.A.
1995: Sensitivity of climate simulations to the parameterization of
convection in the Canadian Climate Centre general circulation model. Atmos.
Ocean, 33, 407-446.
CMIP Documentation Directory
Last update 15 May, 2002. For questions or comments, contact