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ICBP-Newsletter misunderstandings about the AWI-model



Dear all,

in the latest IGBP GAIM newsletter, James and Jean-Claude presented
some OCMIP-CFC results. There, it was written that

"The AWI-model is an adjoint model, which uses hydrographic and
tracer data in an inverse fashion to compute a mean annual ocean
circulation.
The other models are of the more forward type"

This is not true.
To prevent further misunderstandings and to clear up things I will
explain
briefly what our model really is doing.

First of all, we compute CFC concentrations like anybody else in a
"forward way."
The model we use to perform the OCMIP-simulations is neither doing any
"adjoint"
nor "inverse" calculations.
We calculate OCMIP-tracers with a stationary current field which was
originally established using the adjoint technique.  Data of
temperature, salinity,
alkalinity, PO4, CO2, O2, SiO2, and NO3  were used to determine the
mean, annual
circulation.
NO OTHER TRACER DATA were involved, which means that the velocity field
has never been adjusted in order to reproduce CFC data.

This current field is NOT changed during OCMIP simulations.

The CFC-simulations are calculated strictly forward using the flow
field  calculated
from INDEPENDENT measurements (and so any future OCMIP  experiments will
be)!
The very good results could not be expected because there is absolutely
no tuning
towards measured CFC-distributions.

I hope things are a bit clearer now.

Best regards


Marie -France



- --
Marie-France Weirig

Alfred Wegener Institute for Polar and Marine Research
Columbusstrasse
P.O. Box: 12 01 61
D-27515 Bremerhaven/Germany

Phone: (49) (0)471-4831-367
Fax:   (49) (0)471-4831-149
e-mail: mweirig@awi-bremerhaven.de
http://www.awi-bremerhaven.de
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