Elevation and Atmosphere

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I received this tweet* from Katrina (aka @Astro_yyz), and thank her for the kind wishes. But it got me wondering: what exactly is the difference in atmospheric pressure between sea level and the elevation of Kitt Peak Mountain? To the internet!

The Kitt Peak summit is at an elevation of 2,097 m, just over 2 kilometers above sea level. This is the sign that greets you when you hit the top

Kitt Peak: 6750 feet above sea level

Kitt Peak: 6750 feet above sea level

Sea level atmospheric pressure is (on average) 101.325 kPa (kilo Pascals). The atmospheric pressure reduces as altitude increases, the amount by which can be calculated based on simple physical laws. I used a short derivation of these equations by the Portland State Aerospace Society;^1 their equation 9 gives the value of atmospheric pressure as a function of height:

    \[P=100*\left( \frac{44331.514-height}{11880.516}\right)^{(1/0.1902632)}\]

where ‘height’ is in meters. So subbing in height=2097, the equation gives P=78,543 Pascals, or 78.543 kPa. Therefore, the pressure atop Kitt Peak is:

    \[\Delta P=100\left( \frac{78.543}{101.325} \right) = 77.5\%\]

of the pressure at sea level. Cool! And this lines up nicely with a graph that Wikipedia has:

So does this affect me as Katrina alluded to? It hasn’t so far! and it really isn’t high enough for most people to experience any negative effects (such as dizziness, headache, elevated heart rate). However, walking to the cafeteria every day (up a very slight incline) does seem harder than it should be. Though that may just be because I’m horrendously out of shape.

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* My own twitter account is @jesserogerson, however, for the week of 12-18 May 2014 I was tweeting as @AstroCanada. This is the official account of the Canadian Astronomical Society. Each week a different Canadian astronomer will be tweeting from it.

1. A Quick Derivation Relating Altitude to Air Pressure [PDF], Portland State Aerospace Society, 2004
2. Atmospheric Pressure, Wikipedia, accessed May 2014
3. Effect of High Altitude on Humans, Wikipedia, accessed May 2014

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