computation of potential vorticity in GRADS

[Simon Krichak]

Hi Ilukpitiya
Please find attached script posted by Ron Goodson in 2001.

Best,
    Simon

Simon Krichak,  Principal Research Scientist
 Tel Aviv, Israel.

----- Original Message -----
From: "Ilukpitiya Mudi S P Jayawardena" <imspj at HAWAII.EDU>
To: <GRADSUSR at LIST.CINECA.IT>
Sent: Wednesday, October 03, 2007 7:15 AM
Subject: computation of potential vorticity in GRADS


> Dear all
>
> I want to compute potential vorticity in GRADS using NCEP/NCAR reanalysis
> data. The data set don't have theta surface data.
>
> I can define theta ( Potential temperature ) but I don't know how to
> compute [d(theta)/d(p)] and p is for pressure.
>
> I tried to use the commands
> 'define prs=lev'
> 'define z=prs'
> " define dtheta=cdiff(theta,z)"
>
> it does not work. It says
> ' Error from CDIFF: specification dimension non varying
> Operational error : Error from cdiff function
> Error occurred at column 1
> DEFINE error : Invalid expression.
>
> Please help me
>
> Thanks
>
> Ilukpitiya
>
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