DSET    ^anomalies.dat
UNDEF    99999
TITLE    Sample Model Data 
XDEF     1 linear  1 1
YDEF     1 linear  1 1
ZDEF     1 linear 1 1
TDEF     552 linear 12z01jan1950 1mo

vars 1
anom 0 99 xx
endvars

The above is the control file.

!www.atmos.umd.edu/~gcm ; click 'useful' for lots of fortran info by chian-yi liu and steven chan

!http://grads.iges.org/grads/gadoc/aboutgriddeddata.html#descriptor ; for examples of how to code the open and write commands in fortran, and how to write the associated .ctl file (as above)