earthkit.meteo.vertical.array.relative_geopotential_thickness
=============================================================

.. py:function:: earthkit.meteo.vertical.array.relative_geopotential_thickness(alpha, delta, t, q)

   Calculate the geopotential thickness with respect to the surface on model full-levels.

   :param alpha: Alpha term of pressure calculations
   :type alpha: :class:`array-like`
   :param delta: Delta term of pressure calculations
   :type delta: :class:`array-like`
   :param t: Temperature on model full-levels (K).  First dimension must
             correspond to the model full-levels.
   :type t: :class:`array-like`
   :param q: Specific humidity on model full-levels (kg/kg).  First dimension must
             correspond to the model full-levels.
   :type q: :class:`array-like`

   :returns: geopotential thickness of model full-levels with respect to the surface
   :rtype: :class:`array-like`

   .. rubric:: Notes

   ``t`` and ``q`` must contain the same model levels in ascending order with respect to
   the model level number. The model level range must be contiguous and must include the
   bottom-most level, but not all the levels must be present. E.g. if the vertical coordinate
   system has 137 model levels using only a subset of levels between e.g. 137-96 is allowed.

   ``alpha`` and ``delta`` must be defined on the same levels as ``t`` and ``q``. These
   values can be calculated using :func:`pressure_at_model_levels`.

   The computations are described in [IFS-CY47R3-Dynamics]_ (page 7-8).

   .. seealso:: :obj:`pressure_at_model_levels`