specific_humidity_from_dewpoint

specific_humidity_from_dewpoint(td[, p])

New in Metview version 5.13.0.

Computes the specific humidity from the given dewpoint (td) and pressure (p).

Parameters

• td (number, ndarray or Fieldset) – dewpoint temperature (K)

• p (number, ndarray or Fieldset) – pressure (Pa)

Return type

same type as td or None

The result is the specific humidity in kg/kg units. On error None is returned. The following rules are applied when td is a Fieldset:

• if td is a pressure level Fieldset no p is needed

• if td 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 Fieldset defining the pressure on the same levels as td

• for other level types p must be a Fieldset defining the pressure on the same levels as td

When the result is a Fieldset the ecCodes paramId in the output is set to 133 (=specific humidity).

The computation is based on the following equation:

\[e(q, p) = e_{wsat}(td)\]

where:

• e is the vapour pressure (see vapour_pressure())

• e_wsat is the saturation vapour pressure over water (see saturation_vapour_pressure())

• td is the dewpoint temperature