def angstroem(t, h):
  """Compute the Angstroem index.

  Parameters
  ----------
  t : array
    Noon temperature [C].
  h : array
    Noon relative humidity [%].
  
  Returns
  -------
  array
    Angstoem index value at current timestep.

  Example
  -------
  angstroem(17,42) == 3.1
  """
  return (h / 20) + ((27 - t) / 10)