Hiding in the tundra...[theory?]

Kenelm Philip fnkwp at aurora.alaska.edu
Tue Aug 6 14:33:54 EDT 2002

> but it is also true that as you get further north, air pressures are
> somewhat lower at the same altitude.  By Alaska this certainly ought
> to be noticable.

Well, not very. The pressure difference due to the thinner atmosphere at
high latitudes is a millibar or so, or around 1 per mil (= 0.1%)--and
that applies for the same elevation _and the same temperature_, and also
the same conditions regarding cyclones and anticyclones.

	The North Slope lies at low elevations--the Arctic Coastal Plain
is essentially at sea level. Furthermore, during clear summer weather the
Slope often lies within the Polar High. Finally, air temperatures are
cooler than in similar elevations at lower latitudes. The result is that
atmospheric pressures are normally _higher_ than at lower latitudes at
the same date.

	By the way, note that a few years ago commercial airliners were
unable to land at Fairbanks because a Siberian air mass had moved in, with
no temperature inversion at all, and ground temperatures around -55F. The
result was that pressure was so high that the planes' altimeters were
reading off scale. Temperature wins as against the thinner atmosphere!
According to the local Weather Bureau people, Alaska is one of the few
places in the US where atmospheric pressure often exceeds 31 inches.

	In my opinion, the tundra-hiding behavior of arctic butterflies
has nothing to do with atmospheric pressure--and everything to do with
the obvious fact that there's nowhere else to hide. :-)

							Ken Philip


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