code: def cold_spell_days(tas, thresh='-10 degC', window=5, freq='AS-JUL'):
      r
      t = utils.convert_units_to(thresh, tas)
      over = tas < t
      group = over.resample(time=freq)
  
      return group.apply(rl.windowed_run_count, window=window, dim='time')
docs: r"""Cold spell days
  
      The number of days that are part of a cold spell, defined as five or more consecutive days with mean daily
      temperature below a threshold in °C.
  
      Parameters
      ----------
      tas : xarrray.DataArray
        Mean daily temperature [℃] or [K]
      thresh : str
        Threshold temperature below which a cold spell begins [℃] or [K]. Default : '-10 degC'
      window : int
        Minimum number of days with temperature below threshold to qualify as a cold spell.
      freq : str, optional
        Resampling frequency
  
      Returns
      -------
      xarray.DataArray
        Cold spell days.
  
      Notes
      -----
      Let :math:`T_i` be the mean daily temperature on day :math:`i`, the number of cold spell days during
      period :math:`\phi` is given by
  
      .. math::
  
         \sum_{i \in \phi} \prod_{j=i}^{i+5} [T_j < thresh]
  
      where :math:`[P]` is 1 if :math:`P` is true, and 0 if false.