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The two-dimensional general circulation
ocean model can reproduce the general features of the circulation
and the thermal structure of the upper layers of the ocean and its
seasonal and inter-annual variations. It has, however, systematic
errors, some of which are caused by the coarse vertical and
horizontal resolution: the model thermocline is too diffuse; the
Gulf Stream does not separate at the right location.
The ocean analysis is performed every 10
days, down to a depth of 2000 m. Observational input comes from all
around the globe, but mostly from the tropical Pacific, the
tropical Atlantic and, to an increasing degree, from the Indian
Ocean. In places where the ocean floor is below 2000 m the
information from above 2000 m is “propagated” downwards
by statistical vertical influence functions, similar to those in
the atmospheric data assimilation.
The ocean-atmosphere coupling is
achieved by a two-way interaction: the atmosphere affects the ocean
through its wind, heat and net precipitation
(precipitation-evaporation), whilst the ocean affects the
atmosphere through its SST.
For the seasonal forecasts the interaction
is once a day, while for the EPS forecast it is every hour. This
high-frequency coupling may have some positive impact on the
development of some synoptic-scale systems, such as tropical
cyclones.
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