Wednesday, May 16, 2012


date: Fri, 29 Nov 1996 17:17:05 +0100
from: (Stefan Rahmstorf)
subject: Copenhagen

Dear Millennia friends,

let me inform you that the 'model debate' has come to an end through a meeting we
had in Hamburg last week (see below). Thus we can go ahead with our original
model design, plus we will get help from DKRZ with coupling an ice model to our
Millennia model. This is clearly the best outcome we could have wished for the
success of our project.

On the question of what to do in Millennia 2 we have not had enough discussion yet,
I think, and I hope we will be prepared enough in Copenhagen to come to a good
work programme. The contributions we had so far in our mailbox could perhaps be
summarised as follows.

What we may want to do in Millennia 2:

1. Analysis of "one-way" coupled run (performed as part of Millennia 1), i.e. ocean
model forced with atmos model output but no feedback to atmosphere.
Scientific focus:
- air-sea coupling (compare to fully coupled run)
- decadal ocean variability
- ocean response to coupling: drift
- check sensitivity to ocean time steps (and other parameters?)

2. Initial fully coupled runs to finalise/tune coupled model

3. Preparation/testing of data storage/retrieval/analysis machinery

4. Part way through the run: analysis of short term variability, i.e. ENSO in the model

5. Continue analysis of old ECHAM/LSG run

6. Freshwater sensitivity experiments
Focus: high latitude convection patterns, stability of thc

A comment on our schedule for Copenhagen: is it sensible to have the status
reports on the second day and discuss the future on the first? Maybe it is, given
Hans' absence on thursday afternoon (crazy jet-setter...). Maybe on the first day
everyone can give a very short summary (one overhead slide) of what they have
done, what they will do in the second year of Millennia 1, and what they would like to
do in Millennia 2, without going into any scientific details. Then discussion of
where we should be heading. On day 2 then time to discuss some scientific results.
What do you think?

Look forward to the meeting,


Summary of Meeting at MPI Hamburg, 23.12.1996

Scientists present:
Lennart Bengtson
Klaus Hasselmann
Uwe Mikolajewicz (joined later)
Antonio Navarra
Stefan Rahmstorf
Hans von Storch

This meeting was called to coordinate the plans for long coupled GCM
experiments to be conducted at DKRZ. One such experiment is the European
Union's MILLENNIA project with participation of 10 European laboratories,
which aims to run a coupled model for several thousand years; this project
has been going for almost one year. Other more or less long experiments are
being planned.

Klaus Hasselmann strongly advocated that in view of the high expenses both
in CPU time and model development effort, there should not be too many
different coupled models. While at DKRZ only the ECHAM atmosphere
model is being used, there are four ocean models used in various coupled
experiments: LSG, OPYC, HOPE and MOM. The meeting participants
agreed that it is valuable to have conceptually different ocean models such as
LSG and OPYC, but that HOPE and MOM are conceptually so similar that
it would not be advisable to pursue competing strands of coupled

As both MOM and HOPE have advantages and drawbacks, the meeting felt
that one should aim to combine the best aspects of both models in one
"Euro-model" for coupled experiments. This could either be done by adding HOPE
features into the basic MOM code structure or vice versa, whichever is more
practical. The participants saw the major strength of MOM in its user-friendly
and flexible modular "community model" structure with numerous compile-time
options (different stream function solvers, various tracer mixing
parameterisations including the GM scheme, different tracer advection
schemes and so on). As an advantage of HOPE the well-developed ice model
was mentioned.

To decide on the technical aspects of the future model, a task force is to be
formed which includes interested scientists with a working knowledge of
HOPE and/or MOM; Stefan Rahmstorf was charged with organising this. The
programming work involved would be supported by staff from DKRZ's
"Modellbetreuung" department. The leadership of this long-term model
development project should not be at MPI or DKRZ to avoid a "Hamburg
dominance" in climate modeling, but rather at one of the ocean modeling
centres (AWI, Kiel).

As a more immediate step to support the MILLENNIA project, DKRZ staff
will help to couple a good sea ice model to the global MOM model which is
used for MILLENNIA.


Dr Stefan Rahmstorf
Potsdam Institute for Climate Impact Research (PIK)
PO Box 60 12 03
14412 Potsdam

Tel: +49 331 2781 160 (home: +49 331 715429)
Fax: +49 331 2781 204 (home: +49 331 715429)

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