[MITgcm-support] density of water vapor in atmospheric model

[Yuan Lian]

Hi Jean-Michel,

This is really helpful. I  had atm_Rq =0 in my previous simulations. I 
will correct this and see hot it works.

Cheers,
Yuan

Jean-Michel Campin wrote:
> Hi Yuan,
>
> What we currently use for atmospheric simulation is
> (MITgcm/model/src/calc_phi_hyd.F , lines 343-350):
>   
>> C--     virtual potential temperature anomaly (including water vapour effect)
>>         DO j=jMin,jMax
>>          DO i=iMin,iMax
>>           alphaRho(i,j)=maskC(i,j,k,bi,bj)
>>      &             *( tFld(i,j,k,bi,bj)*(sFld(i,j,k,bi,bj)*atm_Rq+one)
>>      &               -tRef(k) )
>>          ENDDO
>>         ENDDO
>>     
> which accounts for water-vapor (sFld) effects on specific volume 
> when we compute the geopotential.
> (see, e.g, http://mitgcm.org/r2_web_testing/latest/,
>  section 1.4.1.2, equations 1.60 & 1.63)
> with theta' = ( theta*(q*atm_Rq+1)-theta_ref ).
>
> The default value of atm_Rq is zero, and depending on the physics pkg
> and units of q, we currently use:
> atm_Rq=0.6078E-3, (MITgcm/verification/aim.5l_cs/input/data, q in g/kg)
> or 
> atm_Rq=0.6078, (verification/fizhi-cs-32x32x40/input/data, q in kg/kg)
>
> This may not be exactly what you need (other type of gas than air),
> but might be helpfull (I hope).
>
> Jean-Michel
>
> On Wed, Aug 01, 2007 at 04:28:12PM -0700, Yuan Lian wrote:
>   
>> Hi,
>>
>> I am trying to figure out how the atmospheric model of MITgcm treats the 
>> density of air
>> due to the addition of water vapor (salinity in oceanic model). When I 
>> looked at find_rho.F, it didn't
>> calculate the local density with water vapor included if the EOS is 
>> ideal gas. This is ok for Earth's atmosphere
>> since the density of water vapor is much less than that of dry air. 
>> However, in my model, the
>> density of water vapor is equivalent or larger than that of the dry air.
>>
>> Is there anyway I can add the effect of density variation caused by 
>> distribution of water vapor to my model?
>> Any help is appreciated. Thanks!
>>
>> Yuan
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>>     
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