# altimeter_to_station_pressure¶

metpy.calc.altimeter_to_station_pressure(altimeter_value, height)

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.

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 $$(p_{mb})$$

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