note on netcdf 64bit vs netcdf-4 file creation DART

[hkershaw-brown]

noticed this when testing:

direct_netcdf_mod.f90 creates netcdf files in 64bit offset mode:

DART/assimilation_code/modules/io/direct_netcdf_mod.f90

Line 1617 in 62ecfa2

create_mode = ior(NF90_CLOBBER, NF90_64BIT_OFFSET)

netcdf_utilities_mod.f90 creates netcdf files in classic mode

DART/assimilation_code/modules/utilities/netcdf_utilities_mod.f90

Line 2409 in 62ecfa2

function nc_create_file(filename, context)

Do we care about this? I don't know. Just making a note.

running perfect_model_obs:
input state file is netCDF-4 time as unlimited
dart created file from perfect_model_obs has a time dimension but not unlimited. 64-bit offset.

If you create the dart file as netCDF-4 (same as the template file) you get

message: nf90_enddef end define mode: NetCDF: One or more variable sizes viola
 te format constraints

so the 64 bit offset is getting around not having the unlimited dimension.

Originally posted by @hkershaw-brown in #278 (comment)

[hkershaw-brown]

Just a note on this since I just hit this with MITgcm
DIFFER : FILE FORMATS : NC_FORMAT_CLASSIC <> NC_FORMAT_64BIT

should file netCDF format be
A namelist option for DART?
An argument to netcdf_utilities::nc_create_file ?