[MITgcm-support] tracers

[Jean-Michel Campin]

Hi Alan,

if you set PTRACERS_EvPrRn(your_tracer_number) to zero, 
and add an explicit flux for this tracer which would just be
proportional to the run-off input, it should do it, no ?
Cheers,
Jean-Michel

On Wed, Sep 23, 2009 at 10:06:44AM +0200, Dimitris Menemenlis wrote:
> Alan, I tried to send this yesterday from hotel but internet crashed.   
> My answer is superseded by Martin's much more useful one.  Here it is  
> nevertheless:
>
> I think that the best you can do is to add a passive tracer with  
> concentration proportional to relative volume of runoff entering a  
> particular surface grid box at a particular time step.  As soon as the  
> runoff enters a model grid box, it mixes completely with the water in  
> that grid box (since a grid box is the smallest volume of water that the 
> model knows of) so adding a passive tracer with the correct  
> concentration in that grid box would be equivalent to what you describe 
> in your message.
>
> Dimitris
>
> On Sep 23, 2009, at 9:28 AM, Martin Losch wrote:
>
>> 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
>> place would be S/R PTRACERS_FORCING_SURF:
>> 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.
>>
>> Martin
>>
>> 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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