[MITgcm-support] hfac question

[Matthew Mazloff]

Hi David,

Yeah, using hFacC for transport on the open boundaries seems  
consistent with my understanding of the implementation.  I think you  
are correct that the value of  hFacW came from periodicity -- but is  
not relevant to the prescription of OBCS values, and this is why hFacC  
is used.

I believe this must be why when one uses OBCS they should have  
Depth(1,:) = Depth(2,:).  So that hFacW(2,:) = hFacC(1,:) and  
everything remains consistent.

-Matt




On Oct 6, 2009, at 9:28 AM, David Hebert wrote:

> Matt,
>
> Along those lines, I notice in obcs_calc.F, for the balance  
> routines, that hFacC's are used instead of hFacW for E/W boundary  
> and hFacS for N/S boundaries. Could that also be related to the  
> hFacW and hfacC assuming periodic BC/s?
>
> Thanks,
>
> David
>
> On 10/06/09 11:09, Matthew Mazloff wrote:
>> Hi David,
>>
>> It is a bit odd that it gave you 90 for hFacW(1,:), but I guess it  
>> is fine as I believe what happens on the western open boundary is  
>> that it sets U(1,:) and U(2,:) to the prescribed value and sets  
>> (assumes) zero divergence right on the boundary center (helps  
>> pressure solver).  So yes, I believe what is truly coming into the  
>> dynamics -- and what is entering the domain -- is  
>> sum(U(2,:).*drF .* hfacW(2,:)).
>>
>> -Matt
>>
>>
>> On Oct 6, 2009, at 8:56 AM, David Hebert wrote:
>>
>>> Hi Matt,
>>>
>>> The point I mentioned is a W boundary point (should  have noted  
>>> that before, sorry). All surrounding points  are  also 100m. I do  
>>> note that the Eastern boundary is 90m. So if hFacW will obtain  
>>> depth on Eastern bounary is there something different I should do  
>>> on the West? i.e., seems I should use hFacW(2,:)?
>>>
>>> Thanks
>>>
>>> David
>>>
>>> On 10/06/09 10:49, Matthew Mazloff wrote:
>>>> Hi David,
>>>>
>>>> This is correct.  You must have sloping topography and the depth  
>>>> at the west side of the cell is 90m, while its 100m in the  
>>>> center.  U is calculated on the west face, so the total volume  
>>>> transport is
>>>> sum(U(1,:).*drF .* hfacW(1,:)).
>>>>
>>>> Likewise one should use hFacS for V transport.
>>>>
>>>> -Matt
>>>>
>>>>
>>>> On Oct 6, 2009, at 8:38 AM, David Hebert wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> I am attempting to balance barotropic inflow/outflow on the  
>>>>> boundaries of a 2D simulation. I ran the model one timestep to  
>>>>> obtain the hFac's in order to more accurately determine the  
>>>>> depth the model uses. The result from Depth.data at one point is  
>>>>> 100m.
>>>>>
>>>>> In order to balance U, according to manual, I would use hFacW. I  
>>>>> get a very different result if I do sum(drF * hFacW). Results  
>>>>> from matlab (for 2D hFac's)...
>>>>>
>>>>> sum(drF .* hfacW(1,:)) = 90
>>>>> sum(drF .* hfacC(1,:)) = 100
>>>>>
>>>>> Seems I don't quite understand hfacW. Any ideas on what I did  
>>>>> wrong here?
>>>>>
>>>>> Thanks
>>>>>
>>>>> David
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> MITgcm-support mailing list
>>>>> MITgcm-support at mitgcm.org
>>>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>
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