code: def exner_function(pressure, reference_pressure=mpconsts.P0):
      r
      return (pressure / reference_pressure).to('dimensionless')**mpconsts.kappa
docs: r"""Calculate the Exner function.
  
      .. math:: \Pi = \left( \frac{p}{p_0} \right)^\kappa
  
      This can be used to calculate potential temperature from temperature (and visa-versa),
      since
  
      .. math:: \Pi = \frac{T}{\theta}
  
      Parameters
      ----------
      pressure : `pint.Quantity`
          The total atmospheric pressure
      reference_pressure : `pint.Quantity`, optional
          The reference pressure against which to calculate the Exner function, defaults to P0
  
      Returns
      -------
      `pint.Quantity`
          The value of the Exner function at the given pressure
  
      See Also
      --------
      potential_temperature
      temperature_from_potential_temperature