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CERFACS seasonal forecast model couples the atmosphere model from Météo-France
(ARPEGE) and the ocean model from LODYC (ORCA)
through the OASIS coupler (Valcke et al., 2000). It was spun up from Antonov
et al. (1998) for temperature and salinity and from rest for the velocities,
using a blended climatology of ERS and in situ (mostly TAO) observed
winds, ERA15 heat fluxes and Xie and Arkin (1996) precipitation and evaporation
data. After this two-year spin up, during which the state remained close
to the climatology, the model was forced with ERA40 daily fluxes, winds,
and with a 200 W/m2/K restoring SST term from November 1986 onwards. The
ocean initial conditions have been produced at CERFACS and shared with
LODYC. They have been obtained by running the ORCA model in forced mode.
In order to produce perturbed ensembles of ocean initial conditions, an
initial condition from the unperturbed forced ocean run is used every
3 months to start two wind-perturbed forced runs. Two weeks before the
target date, four SST perturbations are linearly added and subtracted
during 7 days to the restored SST and then persisted. This procedure has
been chosen in order to preserve the dynamical balance in the mixed layer
scheme of the ORCA model, which would be damaged by a brutal introduction
of the perturbations.
Antonov, J., S. Levitus, T. P. Boyer, M. Conkright, T. O' Brien and C.
Stephens, 1998. World Ocean Atlas 1998. NOAA Atlas NESDIS 27 to 35.
Valcke, S., L Terray and A Piacentini, 2000. OASIS: Ocean Atmosphere
Sea Ice Soil version 2.4, User's guide, CERFACS internal report No TR/CGMC/00-10.
Xie, P. and P. Arkin, 1996. Analyses of global monthly precipitation
using gauge observations, satellite estimates, and numerical model predictions.
J. Climate, 9, 840-858.
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