Relative Humidity¶

Performs a variable conversion from specificHumidity (or mixing ratio), temperature, and pressure to relative humidity. The newly calculated variable is included in the same obs space.

Transform: RelativeHumidity

obs filters:
- filter: Variable Transforms
  Transform: RelativeHumidity
  Method: UKMO
  Formulation: Sonntag

Observation parameters needed (JEDI name)

specificHumidity (\(q\))
airTemperature (\(T\))
pressure or stationPressure (\(P\))
waterVaporMixingRatio (\(w\)) (needed when using Method: UKMOmixingratio)

Method(s) available

Various methods are available, shared across all center options. (Any setting of METHOD will result in using formulations associated with the method.) Setting METHOD can be omitted.

options:

methodDEFAULT
methodUKMOmixingratio
methodUKMO

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: Variable Transforms
  Transform: SpecificHumidity
  Method: UKMO
  Formulation: Sonntag

Observation parameters needed (JEDI name)

relativeHumidity (\(Rh\))
airTemperature (\(T\))
pressure or stationPressure (\(P\))

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.