[MITgcm-support] staggerTimeStep and advection scheme

[samar khatiwala]

Hi Jean-Michel

On Thu, 28 Apr 2005, Jean-Michel Campin wrote:

> Nothing has changed since 21 Sep 2004, and regarding staggerTimeStep,
> I would recommend to look at the documentation since this part
> has been updated in October 2004.

Thanks for pointing me to the documentation. It clarified many things
for me, in particular the ever more convoluted calling sequence. But
(unfortunately for you), not all.

I am still trying to reconcile what you said about using staggertimestep
with certain advection schemes. In particular, if the primary purpose is
to deal with the internal wave stability criterion, can this flag be safely
turned OFF when using adams-bashforth timestepping? I realize this may not
have a simple or short answer, but for people like me who are clueless
about numerical methods, could you suggest a "rule of thumb" for when
this flag should be used and when not.

(Think of this as an entry in a future "MITgcm for dummies" book.)

Apologies for being so dense.

Samar

> > 1) When and for what quantities is staggerTimeStep used (or should be
> >    used)?
> quoting the documentation:
> ``The corresponding calling tree is given in 2.7. The staggered algorithm is
> activated with the run-time flag staggerTimeStep=.TRUE. in parameter file data,
> namelist PARM01''
> And I can add: " ... is activated if and only if the run-time flag
> staggerTimeStep=.TRUE is set in parameter file data"
>
> > 2) Is it used only for active tracers (T/S) and velocity?
> see documentation for what Synchronous time-stepping / staggerTimeStep
> means. Note that passive tracers are stepped-forward within
> the same S/R as active tracers, in THERMODYNAMICS.
>
> > 3) Is it only used for advection schemes 77,33,30?
> cf point 1
>
> > 4) Does it get turned off when adams bashforth is used, since my
> >    understanding is that it is there for internal wave stability.
> >    (I don't see this being done in the code, though.)
> >    In which case, why is it used for ptracers?
> cf point 1.
>
> if something is wrong, or not clear in the documentation, please
> let us know.
>
> Thanks,
>
> Jean-Michel
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