code: def winter_rain_ratio(pr, prsn=None, tas=None):
      
      ratio = liquid_precip_ratio(pr, prsn, tas, freq='QS-DEC')
      winter = ratio.indexes['time'].month == 12
      return ratio[winter]
docs: Ratio of rainfall to total precipitation during winter
  
      The ratio of total liquid precipitation over the total precipitation over the winter months (DJF. If solid
      precipitation is not provided, then precipitation is assumed solid if the temperature is below 0°C.
  
      Parameters
      ----------
      pr : xarray.DataArray
        Mean daily precipitation flux [Kg m-2 s-1] or [mm].
      prsn : xarray.DataArray
        Mean daily solid precipitation flux [Kg m-2 s-1] or [mm].
      tas : xarray.DataArray
        Mean daily temperature [℃] or [K]
      freq : str
        Resampling frequency
  
      Returns
      -------
      xarray.DataArray
        Ratio of rainfall to total precipitation during winter months (DJF)