Thursday, May 30, 2013

Clouds Eats Mountain! Film at 7

I came across this picture of Sierra Blanca near Ruidoso, NM last night.  The peak of Sierra Blanca sits at 11,981 feet, above sea level more than 4,000 feet above Alto, NM where the picture was taken.  As a kid, growing up in Ruidoso, we'd say things like, "Wow, that cloud just hunkered down on top of the mountain." just assuming the cloud had come from somewhere else.  Looking at how the cloud above seemed to be literally streaming into the peak, I wondered if there was some kind of sciencey correlation between clouds and mountains.  I found the answer in an article from the February, 1901 issue of "The School World" by George Chisholm[1] that explained mountains actually help to form clouds, not attract them from afar.

Here's how it works.  Wind carries air saturated with water vapor into the mountain where it is forced up the slope.  As the air rises it expands due the lower air pressure, and as it expands, it becomes colder.  As it cools, the temperature of the air can drop below the saturation point for water vapor causing the vapor to condense into water droplets and it is these water droplets that actually form the cloud.  Mr. Chisholm points out
"It is very important however, that boys and girls should at least get a firm hold of the fact that air (like other gases) cools in expanding, even though it is not necessary in teaching geography to explain how this effect is brought about.  It is not very easy to illustrate this effect in a class, but it may serve to impress the fact on the minds of boys and girls to let them know that some freezing machines are based on this principle, and that all those who cycle may observe for themselves the opposite effect, that of heating by compression, by feeling the bottom their inflator when pumping up their tyres." 
Here's a closer look at the streams coming off the peak.

1.  On cloud formation and other geography test errors

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