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

Method¶

Height \(z\) (m) is computed from pressure \(p\) (Pa). Two methods are available: UKMO and NCAR.

The following constants are used in the calculations:

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

UKMO

\(p > p_l\):

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

\(p_u < p < p_l\):

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

\(p < p_u\):

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

NCAR

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

\(p > 120\) hPa:

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

\(p_u < p < 120\) hPa:

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

\(p < p_u\):

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