View Full Version : Thinner air at higher latitudes

2012-Jun-17, 02:12 PM
article from USA TODAY:
4 climbers presumed dead after avalanche

mount McKinley also known as Dinali, is Americas tallest peak. We'll not a particularly tall pizza global standards, it's latitude makes for far thinner hair than is found in mountains closer to the equipment.

OK, that was Siri's version.

Mount McKinley, also known as Denali, is America's tallest peak. While not a particularly tall peak by global standards, its latitude makes for far thinner air than is found in mountains closer to the equator.
Just how thin is it? And what is the cause? It's colder overall, so it's thinner? Gravity is less at the equator so more/less air? Google is not much help, it just assumes I mean "higher altitudes".

2012-Jun-17, 03:16 PM
Try searching the web for how much the atmosphere deforms as a result of the rotation of the Earth. (I'm only guessing that this is the reason. I haven't researched it myself.)

2012-Jun-17, 03:37 PM
This might be the source of the statement:
The Determination of Pressure Altitude and Implications for High Altitude Physiology (http://www.cohp.org/ak/notes/pressure_altitude_v6.html)

From the linked page:
The current work does not use latitude/season pairs as the independent variable for determining which atmospheric model is applicable to a specific montane setting. Instead, we derive the exact equations that specify how temperature of the air column determines pressure altitude; and then apply these equations to specific mountains during their optimal climbing season.

Looks like something you could sink your teeth into. :)

2012-Jun-17, 04:02 PM
This might be the source of the statement:
The Determination of Pressure Altitude and Implications for High Altitude Physiology (http://www.cohp.org/ak/notes/pressure_altitude_v6.html))After a superficial perusal, I think the paper in the link claims that latitude does make a theoretical difference, but it has negligible practical implications for climbing.

It took me some while to realize that the thread title was not the unsurprising "Thinner air at higher altitudes". Duh.

Ara Pacis
2012-Jun-17, 06:13 PM
The Tropopause (http://en.wikipedia.org/wiki/Tropopause) is lower towards the arctic than at the equator for thermal reasons. I suspect that the increased density lowers the altitude for all pressure-related phenomenon.

2012-Jun-17, 06:19 PM
A cold atmosphere is denser, "thinner", and thus has a steeper pressure gradient; e.g., clouds are lower in the polar latitudes than in the tropics, as is the snow line. This is one reason why upper-air "cold lows" frequently cause bad weather in the lower latitudes; the relatively cooler upper-level air pool has a steeper lapse rate than the warmer air around it, generating convective instability. In a related vein, all the polar jet stream really is, is the boundary between the thinner polar atmosphere and the thicker temperate one.

2012-Jun-17, 06:24 PM
There are standard atmospheres (basically a mix of statistical and thermodynamic models of pressure, density, and temperature vs altitude) for different lattitudes, mostly driven by temperature lapse rates. Mostly, these are for predicting aircraft performance, but since our need for oxygen is not too dissimilar to that of an aircraft engine's need for it, they're pretty good approximations of physiological needs.