Moisture flux convergence

[Mark Schuster]

Hi

I had the same problem before.

Try using this line instead...

> 'qu=vint(pres.5(z=1)/100.,shum.2*uwnd.3,300)'
> 'qv=vint(pres.5(z=1)/100.,shum.2*vwnd.4,300)'

The prob arises since your pressure file only has 1 level while the other ones
have multiple levels.  The division by 100 is there in order to convert the
pascals to mb, which the vint function requires.

Sometimes, the order of opening the files seems to make a difference.  If I
first open the pressure file, it doesn't work, but doing it last (as you have)
does work.

Good luck with your research!

Mark

Quoting "Adam K. Gobena" <agobena at UALBERTA.CA>:

> Hi,
> I would like to compute the vertically integrated moisture flux
> convergence between the surface and the jetstream level. I am using Grads
> for Windows V1.811 and the NCEP/NCAR Reanalysis data (NetCDF format). I
> used the following script to open the data in the order of specific
> humidity, u-wind, v-wind and surface pressure.
>
> 'sdfopen home/mfc/shum.ncep.nc'
> 'sdfopen home/mfc/uwnd.ncep.nc'
> 'sdfopen home/mfc/vwnd.ncep.nc'
> 'sdfopen home/mfc/pres.ncep.nc'
>
> 'set lon x1 x2'
> 'set lat y1 y2'
> 'set t 1 T'
> 'set z 1'
> 'qu=vint(pres.5,shum.2*uwnd.3,300)'
> 'qv=vint(pres.5,shum.2*vwnd.4,300)'
> 'vimf=-hdivg(qu,qv)'
>
> 'd vimf'
>
> When I run the script, the program crushes after the following message.
> ------------------------------
> ga-> run home/mfc/vimfc.txt
> Scanning self-describing file:  home/mfc/shum.ncep.nc
> Found 1 data variables in SDF file.
> Found displayable variable shum with 8 levels in SDF file.
> Scanning self-describing file:  home/mfc/uwnd.ncep.nc
> Found 1 data variables in SDF file.
> Found displayable variable uwnd with 8 levels in SDF file.
> Scanning self-describing file:  home/mfc/vwnd.ncep.nc
> Found 1 data variables in SDF file.
> Found displayable variable vwnd with 8 levels in SDF file.
> Scanning self-describing file:  home/mfc/pres.ncep.nc
> Found 1 data variables in SDF file.
> Found displayable variable pres with 0 levels in SDF file.
> gxstart=0, gxstop=53, gystart=0, gystop=27.
> gzstart=0, gzstop=1, gtstart=0, gtstop=1.
> ----------------------------------
>  Would this be because the surface pressure level in the NCEP Reanalysis
> is set to 0? That is, with z set to 1, the level is set to the minimum
> level of 1000mb in the pressure level files but that of the surface
> pressure remains 0. Any help is greatly appreciated.
>