code: def av(self, data, lon_str=LON_STR, lat_str=LAT_STR,
             land_mask_str=LAND_MASK_STR, sfc_area_str=SFC_AREA_STR):
          
          ts = self.ts(data, lon_str=lon_str, lat_str=lat_str,
                       land_mask_str=land_mask_str, sfc_area_str=sfc_area_str)
          if YEAR_STR not in ts.coords:
              return ts
          else:
              return ts.mean(YEAR_STR)
docs: Time-average of region-averaged data.
  
          Parameters
          ----------
          data : xarray.DataArray
              The array to compute the regional time-average of
          lat_str, lon_str, land_mask_str, sfc_area_str : str, optional
              The name of the latitude, longitude, land mask, and surface area
              coordinates, respectively, in ``data``.  Defaults are the
              corresponding values in ``aospy.internal_names``.
  
          Returns
          -------
          xarray.DataArray
              The region-averaged and time-averaged data.