earthkit.meteo.thermo.array.dewpoint_from_relative_humidity
===========================================================

.. py:function:: earthkit.meteo.thermo.array.dewpoint_from_relative_humidity(t, r)

   Compute the dewpoint temperature from relative humidity.

   :param t: Temperature (K)
   :type t: :class:`array-like`
   :param r: Relative humidity (%)
   :type r: :class:`array-like`

   :returns: Dewpoint temperature (K). For zero ``r`` values returns nan.
   :rtype: :class:`array-like`

   The computation starts with determining the the saturation vapour pressure over
   water at the dewpoint temperature:

   .. math::

       e_{wsat}(td) = \frac{r\; e_{wsat}(t)}{100}

   where:

   * :math:`e_{wsat}` is the :func:`saturation_vapour_pressure` over water
   * :math:`td` is the dewpoint.

   Then :math:`td` is computed from :math:`e_{wsat}(td)` by inverting the
   equations used in :func:`saturation_vapour_pressure`.