Height from pressure

This transform computes height from pressure.

Variables used

  • Pressure (Pa)

Parameters

  • height coordinate: Height coordinate name.

  • height group: Height coordinate group.

  • pressure coordinate: Pressure coordinate name.

  • pressure group: Pressure coordinate group.

Example yaml block

obs filters:
- filter: Variable Transforms
  Transform: HeightFromPressure
  Method: UKMO
  height coordinate: height
  height group: ObsValue
  pressure coordinate: pressure
  pressure group: MetaData

Methods

Height \(z\) (m) is computed from pressure \(p\) (Pa). There are two methods available: The default method uses the standard ICAO atmosphere. The NCAR method uses a fast approximation for pressures > 120 hPa.

The following constants are used in the calculations:

  • \(g\): gravitational constant = 9.80665 m/s2

  • \(r_d\): specific gas constant for dry air = 287.05 J/K/kg

  • \(p_l\): ICAO lower tropopause pressure = 226.32 hPa

  • \(p_u\): ICAO upper tropopause pressure = 54.7487 hPa

  • \(z_l\): ICAO lower tropopause height = 11000.0 m

  • \(z_u\): ICAO upper tropopause height = 20000.0 m

  • \(L_l\): ICAO lower tropopause lapse rate: 0.0065 K/m

  • \(L_u\): ICAO upper tropopause lapse rate: -0.001 K/m

  • \(T_s\): ICAO surface temperature = 288.15 K

  • \(T_i\): ICAO isothermal layer temperature = 216.65 K

Default

  • \(p > p_l\):

\[z = [1.0 - (p / p_l)^{L_l / (g / r_d)}] \times T_s / L_l\]

  • \(p_u < p < p_l\):

\[z = [\log(p_l) - \log(p)] \times T_i / (g / r_d) + z_l\]

  • \(p < p_u\):

\[z = [1.0 - (p / p_u)^{L_u / (g / r_d)}] \times T_i / L_u + z_u\]

NCAR

The NCAR-RAL method: a fast approximation for pressures > 120 hPa. At pressures \(\leq\) 120hPa (~15km) use the ICAO atmosphere.

  • \(p > 120\) hPa:

\[z = 44307.692 \times (1.0 - (p / 101325)^{0.19})\]

  • \(p_u < p < 120\) hPa:

\[z = [\log(p_l) - \log(p)] \times T_i / (g / r_d) + z_l\]

  • \(p < p_u\):

\[z = [1.0 - (p / p_u)^{L_u / (g / r_d)}] \times T_i / L_u + z_u\]