[MITgcm-support] ALLOW_ADDFLUID option and U, V momentum equation

[Angela Marie Zalucha]

For Mars the atmosphere (composed of CO2) can condense and sublimate. 
Usually we assume that if a parcel of atmosphere reaches the condensation 
temperature, it instantaneously drops to the surface.  So in that case if 
the parcel was moving (and therefore contained momentum), when it fell on 
the ground it would come to rest, transfering its momentum to the surface 
and removing it from the atmosphere.  The momentum effect is ignored in 
Mars GCMs.

   Angela




On Fri, 26 Aug 2011, Jason Goodman wrote:

> The source/sink terms affect the momentum equation through the pressure 
> field.  If I have a tank of water with a hose running into it, how does the 
> water already in the tank "know" to move away from the hose spigot? 
> Pressure.  Adding fluid increases the pressure at the source, which causes a 
> pressure gradient pushing nearby water away.
>
> The standard MITGCM solves to find the pressure field needed to make the 
> velocity field non-divergent.  When ALLOW_ADDFLUID is on, it solves for the 
> pressure field needed to make the velocity field have a prescribed 
> divergence: that pressure field then appears in the momentum equation to push 
> water around.
>
> I don't think there *should* be any other terms added to the momentum 
> equations.
>
> JCG
>
> On 8/26/2011 12:44 PM, Angela Marie Zalucha wrote:
>> Kumar,
>> 
>> You're right, the fluid source/sink is assumed not to affect the momentum 
>> equations.  For planetary applications this term is small, I don't know 
>> about the ocean.
>>
>>   Angela
>> 
>> 
>> 
>> On Thu, 25 Aug 2011, Krishnakumar Rajagopalan wrote:
>> 
>>> Hi All,
>>> 
>>> We have been customizing the 4x4 global ocean simulation 
>>> (tutorial_global_oce_latlon) to include sources/sinks  using the 
>>> ALLOW_ADDFLUID option. Checking with grep " ALLOW_ADDFLUID"  *.F,  it 
>>> seems that  sources do not explicitly appear in the U or V momentum 
>>> equations.  If indeed these equations are formally unchanged when the 
>>> source/sink switch is on,  are we correct assuming that this version of 
>>> MITgcm does not have a provision for (input) source momentum? A source 
>>> could have an initial vertical momentum as well, although such cases may 
>>> be more relevant for non-hydrostatic runs.
>>> Thanks a lot
>>> Kumar
>>> 
>> 
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>> Angela Zalucha, Ph.D.
>> Postdoctoral Associate
>> Department of Earth, Atmospheric,
>>   and Planetary Sciences
>> Massachusetts Institute of Technology
>> 
>> Office located at Southwest Research Institute
>> 1050 Walnut Street, Suite 300
>> Boulder, CO 80302
>> USA
>> (720) 208-7211
>> 
>> 
>> http://web.mit.edu/azalucha/www/index.html
>> _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
>> 
>> 
>> 
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>
>

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Angela Zalucha, Ph.D.
Postdoctoral Associate
Department of Earth, Atmospheric,
   and Planetary Sciences
Massachusetts Institute of Technology

Office located at Southwest Research Institute
1050 Walnut Street, Suite 300
Boulder, CO 80302
USA
(720) 208-7211


http://web.mit.edu/azalucha/www/index.html
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