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

[Jean-Michel Campin]

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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