[MITgcm-support] tracers

Martin Losch Martin.Losch at awi.de
Wed Sep 23 03:28:55 EDT 2009

Hi Alan,

I am not sure if I understand exactly, what you want to do exactly,  
but (if you are using pkg/exf) there is a field called runoff (units  
are m/s). All you need to do is add this to a ptracer-field, the best  
surfaceForcingPTr(i,j,bi,bj,iYourTracer) =  
runoff(i,j,bi,bj)*_ra(i,j,bi,bj) * drF(ks)*_hFacC(i,j,ks,bi,bj)
(ks=1 in z-coordinates); because this is an absolute volume add it at  
the end of the routine (to avoid the dilution of volume). Then you'd  
have a volume of freshwater from runoff in m^3 in the ptracer  
iYourTracer (the cell thickness is taken out again when  
surfaceForcingPTr is applied in ptracers_forcing). The disadvantage is  
that you can accumulate more fresh water from runoff in a grid cell  
than the cell can hold which is kind of unsatifactory. Alternatively  
you could add a tracer of some concentration (e.g. 1units/m^3) to the  
run-off, but that appears to me more complicated: In this case I would  
add the tracer at the beginning of the routine as
surfaceForcingPTr(i,j,bi,bj,iTrc) = runoff(i,j,bi,bj) * 1 (units/m^3)
Because this is a now a concentration, it should be diluted by  
additional EmP (but not mR), so that you'd have to remove the runoff  
from the EmPmR and PmEpR in the following lines of code.


On Sep 22, 2009, at 9:51 PM, Alan Condron wrote:

> Does anyone know if it possible to add a tracer directly to the  
> model runoff
> field? For example, instead of adding a ptracer field in a grid cell  
> that
> corresponds to a river mouth, I would like the freshwater that runs  
> off into
> the model in this region to already have a tracer in it. In this  
> way, I will
> know that I'm tagging only freshwater from this source. Is this  
> possible to do?
> Many thanks,
> Alan
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