[MITgcm-support] OBCS

[Martin Losch]

Hi,
now the obcs-package has got me. In the global_ocean.90x40x15 
experiment, I would like to introduce open boundaries in the south 
and/or north to emulate polar regions. Now the simplest and dirtiest 
way to do it would be through restoring in external_forcing. But I want 
to do it the hard and clean way and use the obcs package (o: A few 
questions arise:
1) as a general rule/how-to I start by modifying obcs_calc, so that 
after calling obcs_calc, the boundary values at time myTime+deltaT are 
known. Why myTime+deltaT, why not the current time=myTime?
2) ALLOW_OBCS_SPONGE: Is there code for sponge layers, or am I 
completely responsible for it myself (subroutine obcs_sponge_u/v/t/s)? 
As far as I know, a sponge layer is not much more than a restoring 
zone, correct? If I use a sponge layer (#define ALLOW_OBCS_SPONGE), 
will I still have an open boundary? Or in other words: just having 
restoring in external_forcing.F is not the same as ALLOW_OBCS_SPONGE 
and do the restoring somewhere in obcs_sponge_u/v/t/s, etc? It seems 
so.
3) not quite OBCS, but related. I want to read my open boundary values 
from a file (in calc_obcs), so I have to create code for that, fair 
enough; but because I only want to read one xz-slice, for example, 
(there is even an MDSIOREADFIELDXZ, impressive), I have a problem with 
exchanging the xz-slice, or did I just not find the excange_xz_r? file? 
Does anyone have experience with this?

Martin