[MITgcm-support] global 4deg - more problems

[samar khatiwala]

Hello

I am having a puzzling problem with the global 4 deg verification
experiment.

Based on previous postings from Martin and Chris I ran the model
SYNCRONOUSLY with all deltaT set to 3600. The model blows up within
a few 10's of steps. I asked Martin about this and he assured me
that he routinely runs a 4 deg configuration with this time step.
Indeed, even the 2deg configuration (and all the ECCO stuff) runs
stably with this time step. However, to verify my claim, he checked out
a fresh copy of the MITgcm. It does indeed blow up as advertised.
Changing all time steps to 1200 sec make the model stable.

We thought it might be the initial fast transients that were making the
model unstable. So I ran the model syncronously for 75 years
with all deltaT=1200. This looks fine. Then I changed all deltaT to
3600 and did a pickup. The model blows up again.

Two questions:
1) Does anyone have ideas on what the problem (if indeed there is one)
could be? Perhaps something with the topography?

2) Has anyone ever integrated the MITgcm to complete equilibrium? (The
global 2.8 deg configuration used by several people at MIT (and myself!)
is NOT in equilibrium.) If so, may I please please please get a copy of
your configuration?

Thanks, Samar