[Sharnelle]

Sharnelle asked the Naked Scientists:
   
Hey I'm an Aussie living in Japan and I love your show - great way to keep up on what's happening in the world of science and keeping myself used to hearing English!

We are taught that hot air rises - why is it then that the tops of mountains are always so cold?  Does this have anything to do with altitude and thus the different air pressure?
 
Cheers
Sharnele

What do you think?

[Umby]

Yes, because of pressure.
As a (relatively) warm parcel of air rises, it expands because of the reduction in pressure on that parcel with height.
The molecules within that parcel interact (collide) less with each other which is, by definition, the measure of temperature.
Therefore the temperature is lower for that parcel as some would say it looses heat as it rises.

[litespeed]

There are local exception, however. For instance, I live on top of a small mountain surrounded by other small mountains. The temperature at my house in the morning is often several degrees warmer then the valley below. The valley, just 200 feet lower often is frosted when there is no frost above.

This is an example of cool air dropping into a valley and when elevation change is minor.

[Umby]

Your location being 200 ft. above the valley is roughly the same pressure reading, however in the morning, you would get more sunshine then the valley and earlier.  Also cold (heavy) air in a valley is tough to nudge out unless the wind is really blowing, so it is likely to stick around a little longer.

[litespeed]

Interesting discussion

My temperature probe is on the North side of my house, and is in complete shade almost all the time. In addition, the sun does not come up very early in the Winter. I have a small mountain range to my South which prevents early exposure to the sun itself.

But I keep pondering and am happy to speculate further. It is a curiosity to me. OH! Another curiosity. The road up my 200ft 'mountain' has a South facing microclimate that supports Cudzu in abundance. However, Cudzu has NEVER crossed the road to the higher part of the mountain. And is not found in the Valley at all!

Fascinating curiousities.