Alain Fournier wrote on Sat, 11 Aug 2018
08:57:03 -0400:

On Aug/10/2018 at 9:14 PM, Fred J. McCall wrote :
Alain Fournier wrote on Fri, 10 Aug 2018
19:33:15 -0400:

On Aug/10/2018 at 2:52 PM, Greg (Strider) Moore wrote :
"JF Mezei"* wrote in message ...

And on a more basic question: assuming unlimited supply of compressed
air being shipped to Mars, is it realistic to expect liveable air
pressure at ground when you consider Mar's reduced gravity and how much
more air your would need above you to achieve anything near 14.7psi ?

You know, there's a thriving city here in the US that's a mile up... and
has an average psi of 12psi.
And that's not even all that extreme for human limits.



If you can't achieve proper air pressure at ground, it is worth the
effort to try to terraform the planet since you wouldn't be able to go
outside without a space suit ?

You know, last time I was in Denver, I was wearing shorts and a t-shirt.
(of course the next day I nearly missed my flight due to the snowstorm.)


What you put in parentheses is important. Snow storms are much rarer in
Washington D.C. than in Denver, though they are approximately at the
same latitude. The main reason for that is because you have less air
over your head in Denver, altitude of about 1600m, than in D.C.,
altitude of about 0m. More snow, isn't really the problem here, it is
the cold. If you terraform Mars with less atmospheric pressure than on
Earth you will likely have colder temperatures.


Actually, you get more snow in Denver because of the Rockies. Denver
gets pretty warm in summer, so it's not just thinner air equating to
colder temps.


Correct. There are many things that affect temperatures. Nonetheless,
locations at higher altitudes do tend to have colder temperatures than
locations at lower altitudes. And that is mostly because of thinner air.
And Mars being further away from the sun than Earth, one would prefer
having a "thicker blanket" to help control temperatures.


Some truth there, but the reason you really get that is that it's
easier for ground heat to radiate away at night because there is less
air and it's usually clear. That means there's less heat buildup at
ground level. So Denver gets 100+ temperatures during the day
(because the clear air allows more ground heating) but relatively
cooler temperatures at night (because ground heat can radiate away
more easily through the clear air). You can get the same effect as a
thick air blanket by just having an overcast atmosphere to reflect
heat back toward the ground. Snow off the mountains actually tends to
moderate temperatures in Denver in winter, since that will reflect
heat back toward the ground. Let the air get cold enough to clear a
bit and the snow stops.


--
"Rule Number One for Slayers - Don't die."
-- Buffy, the Vampire Slayer