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

altimeter_to_sea_level_pressure

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:

$$F={[1+\left(\frac{p_0^{n}a}{T_0}\right)\frac{H_b}{p_1^n}]}^{\frac{1}{n}}$$

Where,

$p_0$ = standard sea-level pressure = 1013.25 mb

$p_1=p_{mb}-0.3$ when $p_0=1013.25mb$

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 $(p_{mb})$

$$p_{mb}={[A_{mb}^n-\left(\frac{p_{0}a{H}_b}{T_0}\right)]}^{\frac{1}{n}}+0.3$$