[MITgcm-support] Re: single layer run

[Martin Losch]

Hi Sergey,

I am convinced that even in the case of constant (in time) pressure 
forcing you should end up with a steady state that is non-zero, also in 
the case of a single layer.

Try (possibly in an idealized configuration) starting from rest (ssh = 
0, single layer), without any forcing. The system should remain 
motionless. Then add constant pressure forcing (pLoadFile) in pressure 
units, after adjustment processes have faded away, the circulation 
should be steady (and non-zero), according to the inverted barometer 
effect. If this all works, you know at least that the model has no 
serious problem.

Martin

On May 13, 2005, at 3:52 PM, Sergey Vinogradov wrote:

> Martin:
> I do initialize the experiment with prescribed SSH (which is computed 
> as inverted barometer for the initial atm.pressure). Then the atm. 
> pressure forcing evolves in time and space. I don't have problems with 
> several layers configuration, but in a single-layer setup the model 
> doesn't seem to "feel" the atm. pressure forcing at all, instead, it 
> just solves the problem of the barotropic adjustment of the initial 
> condition. I was thinking if the single layer is really applicable for 
> this type of experiment?
> Regards
> Sergey
>
> Martin Losch wrote:
>
>> Sergey,
>>
>> if you apply pressure forcing that evolves in time, then your flow 
>> field should also vary in time. Even if your pressure forcing is 
>> constant in time (and variable in space), you should reach a 
>> non-trivial steady state (inverted barometer effect), that should 
>> have something like the following balance:
>> f*v + g*d(ssh)/dx + (1/rho0)*dp/dx = 0 (and something similar for the 
>> v-momentum equation, with p=atmospheric pressure), note that the ssh 
>> can (and probably will) be zero in this case.
>> There is  a verification experiment that does this with 4 layers 
>> (inverted_barometer) and constant (in time) forcing. Maybe you can 
>> modify this experiment, or try to see what's different in your case?
>>
>> What do you mean by initial sea-surface height? Do you prescribe an 
>> initial SSH?
>>
>> Martin
>>
>> On May 10, 2005, at 10:47 PM, Sergey Vinogradov wrote:
>>
>>> Hi Ed:
>>> The pressure loading is a realistic variable forcing.
>>> Actually this raises the question if a single layer is a valid 
>>> configuration for such experiment...
>>> Regards
>>> Sergey
>>>
>>> Ed Hill wrote:
>>>
>>>> Hi Sergey,
>>>>
>>>> I've subscribed you to the MITgcm-support email list so that any
>>>> subsequent emails you send will get through.  And I've forwarded 
>>>> your
>>>> email below.
>>>>
>>>> In regards to your question, wouldn't one expect the ocean to reach 
>>>> a
>>>> quiescent (zero-velocity) solution if it were forced with a steady
>>>> atmospheric pressure?  Or are you varying the atmospheric pressure 
>>>> over
>>>> time and space?
>>>>
>>>> Ed
>>>>
>>>> === original message ===
>>>>
>>>> Hello,
>>>>
>>>> After enough playing with a global baroclinic runs, I decided to 
>>>> try a
>>>> barotropic run for which I set eosType to 'linear' and specify a 
>>>> single
>>>> layer with delZ=5000. After several timesteps, the initial 
>>>> sea-surface
>>>> height in the open ocean just dies to zero, while the initial ssh 
>>>> along
>>>> the coasts stays the same. No other terms have been changed from the
>>>> baroclinic experiment setup. Any suggestions how to make it run 
>>>> will be
>>>> greatly appreciated. I forgot to mention that I force the model with
>>>> atmosperic pressure only.
>>>>
>>>> Regards,
>>>> Sergey Vinogradov
>>>>
>>>>
>>>>
>>>
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>>>
>> Martin Losch // Alfred-Wegener-Institut für Polar- und Meeresforschung
>> Postfach 120161, 27515 Bremerhaven, Germany
>> mailto:mlosch at awi-bremerhaven.de // Tel./Fax: ++49(471)4831-1872/1797
>> http://www.awi-bremerhaven.de/People/show?mlosch
>>
>>
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