Moisture flux convergence

[Adam K. Gobena]

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.