[MITgcm-support] oscillating mean flow

[Klymak Jody]

Hi Mark,

On 10-Jun-10, at 8:33 AM, Mark Inall wrote:

> Jody, I tried adding a constant mean flow at the boundaries. This  
> worked fine with f=0: the non-zero U BCs propagated into the domain  
> at the barotropic phase speed. But with rotation, the imposed U- 
> momentum wants to rotate, and then there's a mismatch between the N  
> and S boundaries (at least that's what I think happens) ... that's  
> why I wondered about imposing a cross slice pressure gradient (or  
> moving to a channel with walls) - but I'm not sure how to do that ....

Oh yeah, you are right!  Shouldn't post before coffee...

If your proscribed boundary flow is U_o, then you'd get high in the  
west and low in the east and a southward BT flow.  An eastward bottom  
Ekman layer would allow a steady state and the model is behaving as it  
should.  However, you wouldn't have a mean eastward flow in the  
interior.

I haven't played with it too much, but you should be able to set up a  
body force to mimic a N/S pressure gradient in the interior that would  
set up a eastward mean flow.  Might be hard to match with your E/W  
boundaries though.  I think it can be done in external_forcing.F where  
you would modify gV in your case.  There maybe a better way to do it,  
and to be honest I'm not sure of the units, but I think the docs  
explain it.

Anyways, thats what I'd do.  A steady gV to the north will give you an  
eastwards geostrophically balanced flow.  Cheaper than making a  
channel, but thats your other alternative.

Cheers,  Jody







>
> Mark.
>
>>>> Samar Khatiwala <spk at ldeo.columbia.edu> 10 June 2010 16:00 >>>
> Hi Mark,
>
> Yes, this has been done many times, for e.g., see here: http://www.ldeo.columbia.edu/~spk/Papers/KhatiwalaInternalTidesDSR03.pdf
>
> This is a bit dated, but I know others have implemented it in more  
> recent versions of the code.
>
> Samar
>
> On Jun 10, 2010, at 10:16 AM, Mark Inall wrote:
>
>> Hi,
>>
>> Does anyone have experience with setting up an oscillating mean  
>> flow - either in 2D or in a narrow channel - with rotation?
>>
>> Presently I'm running an oscillating flow over a bump based on the  
>> internal wave verification setup, and I want to add a mean flow -  
>> is the best way to impose a barotropic pressure gradient across the  
>> section and wait for a geostrophic balance??
>>
>> Any thoughts/help much appreciated.
>>
>> Thanks,
>>
>> Mark.
>>
>>
>>
>>
>> Dr Mark Inall
>> Reader in Marine Physics
>> Scottish Association for Marine Science
>> Scottish Marine Institute
>> Oban PA37 1QA
>>
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