The ECBilt-Clio model is a three-dimensional coupled atmosphere-ocean-sea ice model.
The atmospheric component is the ECBilt model (Opsteegh et al. 1998),
a spectral T21 global three level quasi-geostrophic model with simple
parameterizations for the diabatic processes. The dynamical component of the
atmospheric model was developed by Molteni (Marshall and Molteni 1993). The
physical parameterisations are similar as in Held and Suarez (1978). As an extension
to the quasi-geostrophic equations, an estimate of the neglected ageostrophic
terms in the vorticity and thermodynamic equations is included as a time and
spatially varying forcing. This forcing is computed from the diagnostically
derived vertical motion field. With the inclusion of the ageostrophic terms
the model simulates the Hadley circulation qualitatively correct. This results
in a drastic improvement of the strength and position of the jet stream and
the transient eddy activity. Despite the inclusion of these additional terms
the model is two orders of magnitude faster than AGCMs. The model is realistic
in the sense that it contains the minimum amount of physics that is necessary
to simulate the mid-latitude planetary and synoptic-scale circulations in the
atmosphere as well as its variability on various time-scales.
The Clio model (Goosse and Fichefet, 1999) comprises a primitive equation, free-surface
ocean general circulation model coupled to a thermodynamic-dynamic sea-ice model.
The ocean component includes a relatively sophisticated parametrisation of vertical mixing.
A three-layer sea-ice model, which takes into account sensible and latent heat storage
in the snow-ice system, simulates the changes of snow and ice thickness in response to
surface and bottom heat fluxes. In the computation of ice-dynamics, sea ice is considered
to behave as a viscous-plastic continuum. The horizontal resolution of Clio is 3deg in
latitude and longitude and there are 20 unevenly spaced vertical layers in the ocean.
The Clio model has a rotated grid over the North Atlantic ocean in order to circumvent
the singularity at the pole.
The atmosphere and ocean models are
synchronously coupled. The model runs on present generation workstations, taking
0.2 hr cpu time for the simulation of 1 yr (Power Indigo of Silicon Graphics).
A technical description of the atmosphere model can be
found in Haarsma
et al (1996).
References:
Haarsma, R.,
F.M. Selten, J.D. Opsteegh, G. Lenderink and Q. Liu, 1996: ECBilt. A coupled atmosphere ocean
sea-ice model for climate predictability. KNMI, Technical report TR-195.
Held, I.M. and M.J. Suarez, 1978: A two-level primitive equation atmosphere
model designed for climate sensitivity experiments. J. Atmos. Sc., 35, 206-229.
Goosse H. and T. Fichefet, 1999. Importance of ice-ocean interactions for the global ocean circulation: a model study. Journal of Geophysical Research, 104(C10), 23337-23355.
Marshall, J. and F. Molteni, 1993: Toward a dynamic understanding of planetary-scale
flow regimes. J.Atmos. Sc., 50, 1792-1818.
Opsteegh, J.D.,
R.J. Haarsma, F.M. Selten and A. Kattenberg, 1998: ECBilt a dynamic alternative to mixed boundary
conditions in ocean models. Tellus, 50A, 348-367.
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