altimeter_to_station_pressure¶
-
metpy.calc.altimeter_to_station_pressure(altimeter_value, height)[source]¶ Convert the altimeter measurement to station pressure.
This function is useful for working with METARs since they do not provide altimeter values, but not sea-level pressure or station pressure. The following definitions of altimeter setting and station pressure are taken from [Smithsonian1951] Altimeter setting is the pressure value to which an aircraft altimeter scale is set so that it will indicate the altitude above mean sea-level of an aircraft on the ground at the location for which the value is determined. It assumes a standard atmosphere [NOAA1976]. Station pressure is the atmospheric pressure at the designated station elevation. Finding the station pressure can be helpful for calculating sea-level pressure or other parameters.
- Parameters
altimeter_value (
pint.Quantity) – The altimeter setting value as defined by the METAR or other observation, which can be measured in either inches of mercury (in. Hg) or millibars (mb)height (
pint.Quantity) – Elevation of the station measuring pressure
- Returns
pint.Quantity– The station pressure in hPa or in. Hg. Can be used to calculate sea-level pressure.
See also
Notes
This function is implemented using the following equations from the Smithsonian Handbook (1951) p. 269
- Equation 1:
- \[A_{mb} = (p_{mb} - 0.3)F\]
- Equation 3:
- \[F = \left [1 + \left(\frac{p_{0}^n a}{T_{0}} \right) \frac{H_{b}}{p_{1}^n} \right ] ^ \frac{1}{n}\]
Where,
\(p_{0}\) = standard sea-level pressure = 1013.25 mb
\(p_{1} = p_{mb} - 0.3\) when \(p_{0} = 1013.25 mb\)
gamma = lapse rate in [NOAA1976] standard atmosphere below the isothermal layer \(6.5^{\circ}C. km.^{-1}\)
\(t_{0}\) = standard sea-level temperature 288 K
\(H_{b} =\) station elevation in meters (elevation for which station pressure is given)
\(n = \frac{a R_{d}}{g} = 0.190284\) where \(R_{d}\) is the gas constant for dry air
And solving for \(p_{mb}\) results in the equation below, which is used to calculate station pressure \((p_{mb})\)
\[p_{mb} = \left [A_{mb} ^ n - \left (\frac{p_{0} a H_{b}}{T_0} \right) \right] ^ \frac{1}{n} + 0.3\]