def METHOD_NAME(ref_dt, nc_obj, idx):
    """!Get valid time by adding julian days to the reference date time.
    @param ref_dt Datetime object of reference date time
    @param nc_obj NetCDF object
    @param idx index of profile to read
    @returns string of valid time in YYYYMMDD_HHMMSS format
    """
    julian_days = nc_obj.variables['JULD'][idx]
    day_offset = datetime.timedelta(days=float(julian_days))
    valid_dt = ref_dt + day_offset
    return valid_dt.strftime('%Y%m%d_%H%M%S')