[MITgcm-support] rbcs advice

[Jody Klymak]

Hi again,

OK, to answer my own question, no, there is no equivalent of rbcsForcingOffset for obcs.  

Can I suggest in obcs_fields_load.F there be an offset variable, and that this be added to OBCS_PARAMS.h and obcs_readparms.F?  

      CALL GET_PERIODIC_INTERVAL(
     O                  iRecP, iRec0, iRec1, bWght, aWght,
     I                  externForcingCycle, externForcingPeriod,
     I                  deltaTclock, myTime-obcsForcingOffset, myThid )

If you want to use a snapshot, then, it is just a matter of setting 

obcsForcingOffset=-externForcingPeriod/2

Or, one could imagine this being called "externForcingOffset" and being used in "external_fields_load.F" as well....

Cheers,   Jody



On Mar 4, 2014, at  17:52 PM, Jody Klymak <jklymak at uvic.ca> wrote:

> One other quick question that I know has come up before but I can't seem to find...
> 
> I have snapshots at t=0,3600,7200, and I want to use them for my obcs.  However, I seem to remember that externalForcingPeriod=3600 assumes the first file entry is at t=1800, the second at 5400s etc.  Is there an offset to change this so that the first is t=0, etc, or do I have to hack get_periodic_interval.F?  
> 
> Thanks,   Jody
> 
> 
> On Mar 4, 2014, at  9:18 AM, Jody Klymak <jklymak at uvic.ca> wrote:
> 
>> Hi Dimitris,
>> 
>> I wrote you offline as well, but...
>> 
>> On Mar 4, 2014, at  9:06 AM, Dimitris Menemenlis <dmenemenlis at gmail.com> wrote:
>> 
>>> Hi Jody, I think yes.  What grid spacing are you running your regional domain?
>>> And what resolution (space and time) is your open boundary conditions?
>> 
>> Right now I have hourly (well 3720 s to be an even divisor of an M2 tidal cycle) output on a 5- to 1-km grid, with 1 km near my region of interest, and 5 km at the boundaries.  The forcing of this model was an analytical source function (a couple of internal tide line-sources outside the domain), and the model was spun up for 12 tidal cycles allowing reflections from a rough continental slope to set up. Probably accurate out to mode 10 or so.  
>> 
>> I am trying to telescope this down to about 100x200 m in a 50x100 km region to look at the non-linear internal waves on a continental slope.  I nest this inside a 400x300 km region using telescoping resolution, and will initialize and force with the larger 1-km grid. 
>> 
>> All the telescoping is to help make the BCs not too important, but it would be nice to make them as close as possible to reduce reflections. 
>> 
>> Thanks!   Jody
>> 
>>> 
>>> Michael Schodlok has a lot of experience going from
>>> CS510 (18 km) to 1 km domains, then adding tides,
>>> and possibly obcs sponge to get rid of some edge artifacts.
>>> 
>>> But with sufficiently high-resolution (in time) obcs,
>>> I am guessing that you will not need sponging at all.
>>> At least that's the theory.
>>> Chris Hill was experimenting with "replaying" bits
>>> of the 1/48th using obcs.  I don't know how far he got.
>>> 
>>> Let me know if you want to access the 1/48th output
>>> and we can figure out best way to proceed.
>>> 
>>> Cheers, Dimitris
>>> 
>>> On Mar 4, 2014, at 8:50 AM, Jody Klymak <jklymak at uvic.ca> wrote:
>>> 
>>>> Do you think its true that I could just force w/ obcs and do away w/ the sponge? I've used sponges for so long I hadn't thought of giving this a try, but maybe it is all I need to do, and I can ditch rbcs.  Certainly my forcing should have all the modes that could conceivably reach the boundaries by the time my integration is done.  
>>>> 
>>>> Second, 1/48th degree global with tides!  That would be very interesting!
>>> 
>>> 
>>> _______________________________________________
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>>> MITgcm-support at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>> 
>> --
>> Jody Klymak    
>> http://web.uvic.ca/~jklymak/
> 
> 
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