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Saturday, November 6, 2010


A few years ago we had a visit from a friend with a small plane, and when he invited me to go up with him, I jumped at the chance! It was my first time being in the co-pilot's seat, and the fun of the joy-ride for me was heightened by the number and variety of all the switches and dials on the instrument panel, but even more so by the routines and checks my now preoccupied companion was carrying out. I was fascinated with the flight plan he was reporting and the information he was jotting down that was coming from some voice of authority I could hear through his earphones.

It would have been inappropriate to interrupt any of these serious preparations, but I made a some mental notes and, after we successfully landed, I was ready with a few questions. One of them had to do with the dew point. I already knew that the dew point was the temperature at which water molecules slow down so much that they tend to stick to each other instead of bouncing off like they do when they are moving faster at higher temperatures. But why did the pilot need to know the dew point, and why was it reported as an altitude? It turned out that it was just another way of telling him the altitude at which the clouds started forming!

As air rises, it expands and cools down, so this means that at a certain height the temperature reaches the dew point and water vapour condenses. Simple enough - but ever since thinking about it like a pilot, I have taken special delight in looking at clouds. Understanding why they are so often flat lets you observe the normally invisible water vapour in the air appear all at once. The darkness on the bottom of flat clouds is another story for another time.

Just as I find a painting often lets me delight in seeing the world the way the artist was seeing it when he/she created it, so I think scientists can often give us information that allows us to take delight in observing from their informed perspective.

I hope that on a partly cloudy day after this you will find new appeal in looking at the clouds billowing above their flat bottoms. Rie

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