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Computes the equivalent potential temperature from fieldsets on pressure levels. This is a Metview icon function, for detailed documentation please see Potential Temperature.

number dewpoint_from_relative_humidity(t: number, r: number)

vector dewpoint_from_relative_humidity(t: vector, r: vector)

fieldset dewpoint_from_relative_humidity(t: fieldset, r: fieldset)

Computes the dewpoint temperature from the given temperature and relative humidity, where

• • t: temperature (K)
  • r: relative humidity ([0-1])

The result is the dewpoint temperature in K units. On error nil is returned. The computation is based on the following formula:

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

where

• • e_wsat: the saturation vapour pressure over water
  • td: the dewpoint temperature

This functions was introduced in version 5.10.0.

number dewpoint_from_specific_humidity(q: number, p: number)

vector dewpoint_from_specific_humidity(q: vector, p: vector)

fieldset dewpoint_from_specific_humidity(q: fieldset)

fieldset dewpoint_from_specific_humidity(q: fieldset, p: fieldset)

Computes the dewpoint temperature from the given specific humidity and pressure, where

• • q: specific humidity (kg/kg)
  • p: pressure (Pa)

The result is the dewpoint temperature in K units. On error for nil is returned. The following rules are applied when q is a fieldset:

• • if q is a pressure level fieldset no second argument is needed
  • if q is defined on ECMWF model levels (hybrid/eta) p is either a single LNSP (logarithm of surface pressure, identified by paramId=152) field or a fieldset defining the pressure on the levels of q
  • for other level types p is a fieldset defining the pressure on the levels of q

The computation is based on the following equation:

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

where

• • e: the vapour pressure
  • e_wsat: the saturation vapour pressure over water
  • td: the dewpoint temperature

This function was introduced in version 5.10.0.

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