Thank you for replying.Hi, I'm not absolutely certain (as I'm not a software engineer), but I believe the file you're looking for is frame/module_io.F. If that's not it, let me know and I'll try to find out for you. You may also want to take a look in the external/io_* directories.
Thank you.I've reached out to a colleague who knows a bit more about the code structure. They advised that you should look at share/output_wrf.F. This routine calls the write routines in the IO API, and in the case of netCDF output, they are in external/io_netcdf/.