NEWTON:Sea Level to Station Pressure
 
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Name: Ellie
Status: educator
Grade: 9-12
Location: IL
Country: USA
Date: Summer 2014


Question:
I am working on a project with a student that requires atmospheric pressure at different elevations. All I can find in historic data bases is 'sea level' readings. How do I convert back to actual pressure, knowing the elevation of the barometer?


Replies:
Ellie,

Here is a good site:

http://www.altitude.org/air_pressure.php

Here is another good site with Tables and Graphs:

http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

"Absolute" pressure is a pressure reading from 0 pounds per square inch (psi) "Gauge" pressure is a pressure reading on an instrument at the ambient pressure (14.2 psi at sea level). So a gauge reading of 54.2 psi means the absolute pressure is 54.2 - 14.2 =30.0 psi.

Sincere regards, Mike Stewart


Hi Ellie,

Because the pressure changes due to temperature, gravity changes, density and elevation... you should probably take a barometer and measure the pressure at the elevation you are performing the experiment. Usually scientists record the experiment findings along with the temperature and the barometric pressure. Then they convert the experimental findings to Standard Temperature and Pressure, 273K, 100 kPa(0.987 atm), so that comparisons may be made.

Otherwise, you may estimate: P = 101325(1 - H * 2.25577x10E-5)^5.25588 Where P = pressure in Pa and H is height in m.

As a test, use 10,000 m and you should get 26436Pa

Peter E. Hughes, Ph.D., Milford, NH


Ellie,

There are many calculators of sea level pressure on the Internet. You can work backwards from these to get the pressure at an altitude, based on the sea level pressure.

See the section "Altitude atmospheric pressure variation" at the Wikipedia page http://en.wikipedia.org/wiki/Atmospheric_pressure for an equation to calculate pressure at an altitude above sea level.

As the page mentions, for low altitudes (below about 1 km) the pressure decreases almost linearly with altitude 1.2 kPa.

p0 in the equation is the sea level pressure and p is the pressure at the altitude that you're interested in.

1 kPa =10 mb

David R. Cook Meteorologist / Team Lead Atmospheric and Climate Research Program Environmental Science Division Argonne National Laboratory


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