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.. py:function:: relative_humidity_from_specific_humidity(t, q, [p])
*New in Metview version 5.14.0*.
Computes the relative humidity from the given temperature (``t``) and specific humidity (``q``) and pressure (``p``).
:param t: temperature (K)
:type t: number, ndarray or :class:`Fieldset`
:param q: specific humidity (kg/kg)
:type q: number, ndarray or :class:`Fieldset`
:param p: pressure (Pa)
:type p: number, ndarray or :class:`Fieldset`
:rtype: same type as ``t`` or None
The result is the relative humidity in % units. On error None is returned. The following rules are applied when ``t`` and ``q`` are :class:`Fieldset` objects:
* if ``t`` is a pressure level :class:`Fieldset` no ``p`` is needed
* if ``t`` is defined on ECMWF model levels (hybrid/eta) ``p`` must be either a single LNSP (logarithm of surface pressure, identified by paramId=152) field or a :class:`Fieldset` defining the pressure on the same levels as ``t``
* for other level types ``p`` must be a :class:`Fieldset` defining the pressure on the same levels as ``t``
When the result is a :class:`Fieldset` the ecCodes **paramId** in the output is set to 157 (=relative humidity).
The computation is based on the following formula:
.. math::
r = 100 \frac {e(q, p)}{e_{msat}(t)}
where:
* e is the vapour pressure (see :func:`vapour_pressure`)
* e\ :sub:`msat` is the saturation vapour pressure based on the "mixed" phase (see :func:`saturation_vapour_pressure`)
* q is the specific humidity
* p is the pressure
* t is the temperature
.. note::
For :class:`Fieldset` data on pressure and model levels :func:`relative_humidity_from_specific_humidity` gives equivalent results to :func:`relhum`.
.. note::
See also :func:`relhum` and :func:`specific_humidity_from_relative_humidity`.