converting data to *.ctl format for use with traj.gs

[Jason Snyder]

I have a NetCDF data set that is a composite of wind data based on certain
phases of the Madden Julian Oscillation and I was interested in looking at
the backwards trajectories of air parcels coming into Lake Tahoe in such a
scenario.  I have been trying to work with the script traj.gs, but GrADS
said that TDEF is undefined.  I was then told that I need to use a .ctl
file, but how do I convert data in NetCDF format to that that can be used
in a .ctl file which I would need to run the script traj.gs

Thanks,

Jason