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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