CDO

Dear User,
I am trying to open a NetCDF file using GrADS but getting some error message as
"SDF file has no discernable time coordinate -- using default values.".

The NeTCDF file is generated using the GrADS sdfwrite command.
Could you please help me to avoid this error.
The ncdump -h output is provided below.

netcdf SAmask_model {
dimensions:
lon = 291 ;
lat = 210 ;
variables:
double lon(lon) ;
lon:units = "degrees_east" ;
lon:long_name = "Longitude" ;
double lat(lat) ;
lat:units = "degrees_north" ;
lat:long_name = "Latitude" ;
double mask(lat, lon) ;
mask:_FillValue = -999000000. ;
}

Thanks.
SBR