Barometric (corrected) to kPa
by D Krause on 01/26/04 at 12:20:47

The Barometric pressure reported by the weather bureau is corrected for the local altitude creating a standard referenced to sea level. I would like to convert this to actual absolute pressure, what is the pressure change per 1000 meters of change in altitude in kPa.

Re: Barometric (corrected) to kPa
by gunnarm on 02/01/04 at 08:14:42

Pressure change in the atmosphere is not linear. It depends among other things on temperature. The following formula gives the relationship between height (h) over reference pressure surface (Po), mean temperature (To) of air at reference pressure surface and pressure at height above reference surface (P): h = 67,3 x To x log(Po/P) ; (h in meters).

From this it is obvious that not only temperature matters, but also the absolute values of Po and P; the distance between two pressure levels is less if pressures are high (even if the pressure difference is identical).

For practical purposes us private pilots (when flying at low altitudes) use the relationship 30 feet or 10 meters per hPa pressure difference.

Re: Barometric (corrected) to kPa
by gunnarm on 02/13/04 at 07:32:11

My previous answer was slightly wrong; temperature in the formula is MEAN temperature of air between pressure levels P and Po. A better form would thus be:

h = 67.3 x T x log(Po / P) , (h in meters)

In the Standard Atmosphere temperature falls 2 degrees (C or K) per 1000 feet (approx. 330 meters).