code: def format_index(data):
      
      year = data.year.apply(str)
      jday = data.jday.apply(lambda x: '{:03d}'.format(x))
      hours = data.hour.apply(lambda x: '{:02d}'.format(x))
      minutes = data.minute.apply(lambda x: '{:02d}'.format(x))
      index = pd.to_datetime(year + jday + hours + minutes, format="%Y%j%H%M")
      data.index = index
      data = data.tz_localize('UTC')
      return data
docs: Create UTC localized DatetimeIndex for the dataframe.
  
      Parameters
      ----------
      data: Dataframe
          Must contain columns 'year', 'jday', 'hour' and
          'minute'.
  
      Return
      ------
      data: Dataframe
          Dataframe with a DatetimeIndex localized to UTC.