Relative Humidity

Performs a variable conversion from specific_humidity, temperature, and pressure to relative humidity. The newly calculated variable is included in the same obs space.

Transform: ["RelativeHumidity"]

obs filters:
- filter: Variables Transform
Transform: ["RelativeHumidity"]
Method: UKMO
Formulation: Sonntag

Observation parameters needed (JEDI name)

  • specific_humidity (\(q\))

  • air_temperature (\(T\))

  • air_pressure or surface_pressure (\(P\))

Method(s) available

Only one method is avalable, shared accross all center options. (Any setting of METHOD will result in using this unique method.) Setting METHOD can be omitted.

The relative humidity (\(Rh\)) is retrieved as follow:

\[Rh = w/w_{sat}\]

with \(w_{sat}\) (saturated water vapor mixing ratio) derived using \(e_{sat}\) (saturated vapor pressure):

\[w_{sat} = \epsilon \times e_{sat}/(P-e_{sat})\]

and \(w\) (water vapor mixing ratio) derived using \(q\) (specific humidity):

\[w = q/(1-q)\]

\(\epsilon\) is ratio of the gas constant for dry air (\(R_{d}\)) over the gas constant for water vapor (\(R_{v}\)). The value of \(e_{sat}\) (saturated vapor pressure) is derived using Saturated Vapor Pressure from T.

Formulation(s) available

Various formulations are available to derive Saturated Vapor Pressure from T.

Specific Humidity

Performs a variable conversion from relative humidity, temperature, and pressure to specific humidity. The newly calculated variable is included in the same obs space.

Transform: ["SpecificHumidity"]

obs filters:
- filter: Variables Transform
Transform: ["SpecificHumidity"]
Method: UKMO
Formulation: Sonntag

Observation parameters needed (JEDI name)

  • relative_humidity (\(Rh\))

  • air_temperature (\(T\))

  • air_pressure or surface_pressure (\(P\))

Method(s) available

Only one method is avalable, shared accross all center options. (Any setting of METHOD will result in using this unique method.) Setting METHOD can be omitted.

The specific humidity (\(q\)) is retrieved as follows:

\[q = w/(1+w)\]

where water vapor mixing ratio (\(w\)) is derived from relative humidity (\(Rh\))

\[w = Rh \times w_{sat}\]

with \(w_{sat}\) (saturated water vapor mixing ratio) derived using \(e_{sat}\) (saturated vapor pressure):

\[w_{sat} = \epsilon \times e_{sat}/(P-e_{sat})\]

With \(\epsilon\) is ratio of the gas constant for dry air (\(R_{d}\)) over the gas constant for water vapor (\(R_{v}\)). The value of \(e_{sat}\) (saturated vapor pressure) is derived using Saturated Vapor Pressure from T.

Formulation(s) available

Various formulation are available to derive Saturated Vapor Pressure from T.