def get_ctm_nc_var(variable):
    """
    Get number variable for diagnostic family where NetCDF import
    from *.dat file has failed. This function returns a category name + a
    number value to refer to diagnostic ording in NetCDF.

    Parameters
    ----------
    variable (str): NetCDF variable within number suffix

    Returns
    -------
    variable (str): NetCDF variable in GEOS-Chem output

    Notes
    -----
     - This is only called as a back up, and should only be used for test
    ouput and not for production runs

    """
    d = {
        'DAO_3D_S__CMFMC': 'DAO_3D_S___4',
        'DAO_3D_S__DTRAIN': 'DAO_3D_S___3',
        'DAO_3D_S__SPHU': 'DAO_3D_S___2',
        'DAO_3D_S__TMPU': 'DAO_3D_S___1',
        'DAO_3D_S__UWND': 'DAO_3D_S__',
        'DAO_3D_S__VWND': 'DAO_3D_S___0'
    }
    return d[variable]