20010329: gddiag term calculations

Jimmy,

If you don't specify the level of GRDNAM in gddiag, then the LEVEL1 and
LEVEL2 of the resultant grid will be the first 2 levels in the equation
(using gdinfo will show this).

For example, your equation mul(omeg@500,vord) should result in a
grid vorj@500:400 which is probably where you are running in to problems
in the 3rd gfunc expression.

You can work around this in 1 of 2 ways:

1) set the LEVEL1:LEVEL2 in the GRDNAM definition of the output grid

   gfunc = mul(omeg@500,vord)
   glevel = 400:600
   grdnam = vord@400:600 

2) rearrange the multiplication so that 400:600 are the first 2 levels

   gfunc = mul(vord,omeg@500)
   glevel = 400:600
    grdnam = vord


You can explicitly define all of the @, % and ^ inline definitions in the GRDNAM
expression, so you could define a term  as being valid on a different level-
for instance if your result of the equation was surface vorticity using the
sutpet terms, you could have grdnam=vor@0%none.

Let me know if you have further questions.

Steve Chiswell
Unidata User Support




On Thu, 29 Mar 2001, J. Correia wrote:

> i am calculating terms in the vorticity tendency equation...enclosed is my
> script...
> my question is how to get the layer difference terms to carry over into
> other calculations. i thought overspecifying would do it, but im just
> missing something. the terms i have problems with are:
> if ( $gfun ==
> 'quo(ldf(avor),200)' ) then
> set glevel='400:600'
> set grdnam='vord'
> endif
> if ( $gfun == 'mul(omeg@500,vord)' ) then
> set glevel='400:600'
> set grdnam='vorj'
> endif
> if ( $gfun == 'mul(-1,vorj)' ) then
> set glevel='400:600'
> set grdnam='vet2'
> endif
>  the response i get is an error in the multiply command, even when i
> specify the glevel to 500mb....
> any help would be much appreciated...
> i havent seen anything in the help files, but i might be entering the
> wrong key words....
> thanks again...
> jimmyc
> 
> 
>