Pressure from Height (using the ICAO atmosphere)

Converts heights to pressures using the ICAO atmosphere. The newly calculated variable is included in the same obs space.

Transform: PressureFromHeightForICAO

obs filters:
- filter: Variable Transforms
  Transform: PressureFromHeightForICAO

Observation parameters needed (JEDI name)

  • geopotentialHeight (\(Z\))

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. (see formulation for details)

Formulation(s) available

See the unique formulation Heights to pressures (using the ICAO atmosphere) for details

Pressure from Height over a vertical profile

Derive pressure from height for vertical profile (e.g. sonde report). This is especially needed for radiosonde using a 3 09 055 BUFR template.

Transform: PressureFromHeightForProfile

obs filters:
- filter: Variable Transforms
  Transform: PressureFromHeightForProfile
  Method: UKMO

Observation parameters needed (JEDI name)

  • geopotentialHeight (\(Z\))

  • airTemperature (\(T\))

  • dewPointTemperature (\(T_{d}\)) or relativeHumidity (\(Rh\))

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. (see formulation for details)

Nash et al (2011) showed that with GPS heights and accurate temperatures measured pressures are almost redundant and it seems likely that the use of pressure sensors will decrease over time. The pressure can be calculated hydrostatically starting from the station pressure. For two adjacent levels i and i+1 (eg eqn 2.2 of Chouinard and Staniforth, 1995):

\[\frac{Z_{i+1}-Z_{i}}{ln(\frac{P_{i-1}}{P_{i}})} = \frac{-R_{d}(T_{i+1}-T_{i})}{2g}\]

which gives

\[P_{i+1} = P_{i} \times e^{ \frac{2g(Z_{i}-Z_{i+1})}{R_{d}(T_{i+1}-T_{i})}}\]

Where \(R_{d}\) is the specific gas constant for dry air.

For better accuracy one can replace the temperature with the virtual temperature \(T_{v}\):

\[Tv = T \frac{P+\frac{e_{sat}}{\epsilon}}{P+e_{sat}}\]

where \(e_{sat}\) is the saturated vapour pressure which can be calculated from \(T_{d}\) or \(Rh\) using saturation vapor pressure from temperature, and \(\epsilon\)) over the gas constant for water vapor (\(R_{v}\)).

In this equation we use the pressure \(P\) from the previous level as we don’t yet have \(P\) for the current level (this should be a good approximation for the high-resolution reports). Note that if the pressures have been calculated hydrostatically (or from the model height/pressure profile) there is no point in applying the hydrostatic check below.

Formulation(s) available

By default the saturated vapour pressure (\(e_{sat}\)) is derived using the Sonntag formulation of Saturated Vapor Pressure from T.