code: def cloud_cover_to_irradiance_liujordan(self, cloud_cover, **kwargs):
          
          # in principle, get_solarposition could use the forecast
          # pressure, temp, etc., but the cloud cover forecast is not
          # accurate enough to justify using these minor corrections
          solar_position = self.location.get_solarposition(cloud_cover.index)
          dni_extra = get_extra_radiation(cloud_cover.index)
          airmass = self.location.get_airmass(cloud_cover.index)
  
          transmittance = self.cloud_cover_to_transmittance_linear(cloud_cover,
                                                                   **kwargs)
  
          irrads = liujordan(solar_position['apparent_zenith'],
                             transmittance, airmass['airmass_absolute'],
                             dni_extra=dni_extra)
          irrads = irrads.fillna(0)
  
          return irrads
docs: Estimates irradiance from cloud cover in the following steps:
  
          1. Determine transmittance using a function of cloud cover e.g.
             :py:meth:`~ForecastModel.cloud_cover_to_transmittance_linear`
          2. Calculate GHI, DNI, DHI using the
             :py:func:`pvlib.irradiance.liujordan` model
  
          Parameters
          ----------
          cloud_cover : Series
  
          Returns
          -------
          irradiance : DataFrame
              Columns include ghi, dni, dhi