[MITgcm-devel] obcs and passive

[Jean-Michel Campin]

Hi Samar, Martin, and others,

I have no strong objection in having an option to
apply Dirichlet BC at the surface level.

I am just concerned about different interpretations:
> But it also depends on how you think about the Dirchlet BC. My
> viewpoint, ...
and some confusion that could be added.

And also the fact that it will add some complexity to the code
since it will have to be applied several times (like OBC apply): in
multidimensional advection; with convective adjustment by permutation;
and obcs (which one will be applied last, surface or obc ?) but
this last one might not be a big deal.

An other issue is that it might be difficult to get a diagnostics
of the amount of tracer that is added or removed, which is something
that some users would like to have.

Now, in many applications, a strong relaxation term would produce
a similar effect, can still be considered as a forcing term
(the model continue to solve for the tracer concentration
everywhere, including the surface level), is easy to diagnose,
and does not suffer from any ambiguity.
Simply, when the time step is long (as I understand, Samar, this
is your case ?), this restoring term needs to be treated implicitly
(inside implidiff or the others S/R that also deal with implicit
vertical advection).

And to Martin:
> My question: Should I create a new tag (checkpoint57u_post) after
> checking in my code? I am asking because I no longer see a clear
> pattern in when a tag should be created and I don't want to interfere
> with a policy that I maybe should know (but don't) (o:
Yes, it's a good idea.

Jean-Michel