Re: precipitable water

I have attached a simple script.
It creates a 'interface sigma' coordinate. This allows
the 'dpres_hybrid_ccm' function to be used. As you can see,
this offers an alternative to 'prcwater_dp' to calculate
the precipitable water. This uses 'dim_sum_n'
Note there is no need to reorder dimensions. The answers are
the same.

On 2/23/11 12:21 PM, Michael Notaro wrote:
> Dennis, this seems to work. The problem before was
> that dpres_hybrid_ccm produced 17 levels and q
> has 18 levels, so there is an inconsistency in the
> prcwater_dp command. Instead, now I estimate q between
> levels and use the corresponding thicknesses.
>
>
> a=addfile("../con9096/Southwest_ATM.1991070100.nc","r")
> xlat=a->xlat
> xlon=a->xlon
> rcm_map=a->rcm_map
> iy=a->iy
> jx=a->jx
> time=a->time
> q=a->qv ; kg per kg
> ps=a->ps ; hPa
> sigma=a->sigma
> A=a->sigma
> A=0.0
> P0=0.0
> dp_sigma = dpres_hybrid_ccm(ps,P0,A,sigma)
> dp_sigma=dp_sigma*100.
> dp_sigma!0 = ps!0
> dp_sigma!1 = "plevel"
> dp_sigma!2 = ps!1
> dp_sigma!3 = ps!2
>
> q_order=q(time|:,iy|:,jx|:,kz|:)
> dp_sigma_order=dp_sigma(time|:,iy|:,jx|:,plevel|:)
>
> q1=new((/124,148,158,17/),float)
> do iz=0,16
> q1(:,:,:,iz)=(q_order(:,:,:,iz)+q_order(:,:,:,iz+1))/2.
> end do
>
> copy_VarCoords(dp_sigma_order,q1)
>
> pw = prcwater_dp(q1,dp_sigma_order)
> copy_VarCoords(ps,pw)
>
> pw@long_name = "total column precipitable water"
> pw@units = "kg/m2"
> pw@coordinates = "xlat xlon"
> pw@grid_mapping = "rcm_map"
>
> system("rm pw.nc")
> out=addfile("pw.nc","c")
> out->pw=pw
> out->xlat=xlat
> out->xlon=xlon
> out->rcm_map=rcm_map
> out->iy=iy
> out->jx=jx
> out->time=time
>
>
>
>
> On Feb 22, 2011, at 6:24 PM, Dennis Shea wrote:
>
>> One approach
>>
>> [1]
>> http://www.ncl.ucar.edu/Document/Functions/Built-in/dpres_hybrid_ccm.shtml
>>
>> This uses:
>> p(k) = A(k)*PO + B(k)*PS
>> The B(k) are the the sigma levels.
>> A = sigma
>> A = 0.0
>> P0 = 0.0
>> dp_sigma = dpres_hybrid_ccm(ps,P0,A,sigma)
>> dp_sigma!0 = ps!0 ; (say) time
>> dp_sigma!1 = "plevel"
>> dp_sigma!2 = ps!1 ; lat
>> dp_sigma!3 = ps!2 ; lon
>> printVarSummary(dp_sigma)
>>
>>
>> [2]
>> http://www.ncl.ucar.edu/Document/Functions/Built-in/prcwater_dp.shtml
>> pw =
>> prcwater_dp(q(time|:,lat|:,lon|:,sigma|:),dp_sigma(time|:,lat|:,lon|:,plevel|:))
>>
>> pw@long_name = "total column precipitable water"
>> pw@units = "kg/m2"
>>
>>
>>
>>
>> On 02/22/2011 02:36 PM, Michael Notaro wrote:
>>> How can I compute precipitable water
>>> on a lat2d x lon2d grid using sigma
>>> coordinates, given water vapor mixing
>>> ratio output and surface pressure?
>>>
>>> Thanks, Michael

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