[MITgcm-support] ptracer surface boundary condition

[Martin Losch]

Samar,
as far as I can see (and that may not be very far), you can only 
specify pTracer-tendencies (in ptracers_forcing_surf.F)
If you use the gchem package, there is the flag GCHEM_SEPARATE_FORCING. 
If you do not set that, then you have to calculate the gchemTendency in 
gchem_calc_tendency; an example for the is the cfc-pkg, 
(verification/cfc_example), but again it's all tendencies and you 
cannot prescribe the value of the tracer at the surface.
If you set the CGHEM_SEPARATE_FORCING flag, then the ptracers are 
updated a second time after the AB-timestep. In the routine 
gchem_forcing_sep you can do, in principle, anyting to the ptracers you 
like, for example, ptracer(i,j,1,bi,bj,itracer) = some-value and you 
have your Dirichlet-BC, but unless your provide some mechanism in the 
routine yourself, this will be inconsistent with the field for k>1 at 
this time (at the end of the timestep, gchem_forcing_sep is called 
before do_fields_blocking_exchanges and also before do_the_model_io). 
You'll enter the next timestep with this inconsistency at the surface.

Martin

On May 23, 2005, at 7:46 PM, samar khatiwala wrote:

> Hello
>
> I would like to perform some ptracer simulations in which the
> ptracer concentration is prescribed at the surface. This could
> be a time-dependent boundary condition. Unfortunately, I don't
> see any simple way to use existing code to prescribe such a BC.
> Simply setting pTracer(...,k=1,..)=BC does not work all that well.
> To make this work robustly (and consistent with the time stepping) I 
> have
> to intervene at multiple locations in the code to (re)set pTracer and 
> gPtr
> to the BC.
>
> I was wondering if someone has figured out how to do this in a cleaner
> and more consistent manner. Perhaps this could be incorporated into the
> gchem package since it seems like a useful capability to have.
>
> Thanks
> Samar
>
>
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