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[GEMPAK #CIJ-357082]: GDVINT - interpolate other data grids

Hi Steve-

> I am trying to use GDVINT to interpolate from pressure to isentropic 
> coordinates.  I am able to output data successfully, but the output only 
> contains a few parameters (pressure, vertical velocity, Montgomery 
> streamfunction, humidity).
> 
> Is there a way to specify other parameters to interpolate?  For example, the 
> geopotential height of the isentropic surface itself?  This would allow 
> isentropic surfaces (including wind vectors) to be visualized in 3-D in 
> software packages such as Unidata's IDV.

The list of parameters is hard coded, I believe.  I asked NCEP about this a 
while back (because I wanted to do the same thing).  As part of the response, I 
got back:

HGHT is not a parameter that is needed on THTA coordinates. The Montgomery 
Stream Function (PSYM) is the equivalent of HGHT in an isentropic coordinate 
system. If you plot PSYM, it should look like a lot like a height plot on 
pressure coordinates.

There is a way to compute the height from the PSYM. Using gempak terms:

QUO(SUB(pres, MUL(1005,MUL(thta, EXP(QUO(pres,1000),kappa)))), gravty)

This works out to solving the Montgomery Stream Function for height:

Psi = Cp * T + g * z

T = Theta * ( P / P0 ) ^ R/Cp

R/Cp = kappa
Cp = 1005
P0 = 1000

z = 1/g * ( Psi - Cp * T )
  = 1/g * ( Psi - 1005 * Theta * ( P / 1000 ) ^ kappa )


I have not had a chance to try to implement this, though.  For now, using PSYM 
would not work for what you want to do, though.

Sorry I don't have a solution for you at this time.  Better support for 
isentropic coordinates is on the IDV list of things to do, but it will be a 
substantial job and right now we don't have the resources to do it.

Don Murray


Ticket Details
===================
Ticket ID: CIJ-357082
Department: Support GEMPAK
Priority: Normal
Status: Open