A Sublime Day
Today one of my favorite things about Winter in Colorado is happening. It's quite cold today, below freezing; and we have a lot of snow in the ground, the streets, and roofs. But because it's a sunny day; and thanks to our altitude and thin dry air, some of that snow is subliming.
(http://en.m.wikipedia.org/wiki/Sublimation_(phase_transition))
Even though the ambient air temperature is below freezing, the sun absorbed by the dark surfaces provides enough energy for the phase transition. It's forming clouds of water vapor that rise up from places like asphalt covered streets and rooftops where the sun shines on them. It probably happens at lower elevations, too; but the higher you go, the lower the atmospheric pressure, so the more readily water sublimes.
It's a very cool effect. Something like lots of little dry ice fog machines going. I enjoy watching it. (I wanted to include a photo, but it's one of those things that's very hard to photograph).
(http://en.m.wikipedia.org/wiki/Sublimation_(phase_transition))
Even though the ambient air temperature is below freezing, the sun absorbed by the dark surfaces provides enough energy for the phase transition. It's forming clouds of water vapor that rise up from places like asphalt covered streets and rooftops where the sun shines on them. It probably happens at lower elevations, too; but the higher you go, the lower the atmospheric pressure, so the more readily water sublimes.
It's a very cool effect. Something like lots of little dry ice fog machines going. I enjoy watching it. (I wanted to include a photo, but it's one of those things that's very hard to photograph).