On 2005-06-13, Peter Duniho wrote:
"Hilton" wrote in message
ink.net...
How is standard temperature and pressure defined below sea level?

Same as above sea level. Take the standards at sea level, apply a standard
adjustment, viola.

On a point of pedantry, what does a stringed musical instrument, a
little larger than a violin, have to do with the subject at hand? :-)

I know that the gravitation force
starts decreasing in a *linear* fashion below sea level

As far as I know, the difference in gravity has to do with the amount of
mass under you, and is negligible with respect to temperature or pressure.
Same thing would be true of high-elevation terrain.

Especially since airports below MSL aren't that far below MSL anyway
(IIRC, the 'deepest' airport in the continental US is only about -200 MSL,
but the highest, Leadville, has an additional 9000 ft of rock below it).

I've been to a below MSL airport - Thermal (Palm Springs), California.
I didn't notice any difference. But it was kind of neat watching a
correctly set altimeter go below 0 feet :-)

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"