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Blowin' in the Wind, Issue #024 What is the Butterfly Effect in Meteorologty - November 1, 2005
November 01, 2005

The butterfly effect in meteorology

Has anyone ever mentioned the butterfly effect in meteorology before? This article expands on my previous one on the subject, use the link above.

Could a small change in today's weather conditions make a difference later on? A big difference? The answer here is "nothing is impossible".

We call this science "chaos theory". The ridiculous notion of "Does the flap of a butterfly's wings in Brazil set off a tornado in Texas?" has become famous since introduced by scientist Edward Lorenz (without a "t") in 1963. Ok, so he originally used a seagull. But because of that question, chaos theory has become known as the butterfly effect in meteorology.

Now folks, how is this possible? You would think that out of a million wing flaps, each producing a tiny anomaly in the ambient wind, all would disappear forever within a few seconds. You'd probably be right. After all, they're just meaningless eddy currents.

But maybe one stray little atmospheric pressure change could combine with prevailing outside forces which could grow into something more substantial. Something that could cause an extra cloud here, then an upper wind in an unusual place a few days later, and so on until a tornado turns up next year. One which would not have formed otherwise.

Just maybe.

You know what else? They would never be able to pinpoint the cause.

It goes to show how complex weather prediction is. It is impossible to put every detailed element of the so-called initial conditions into a forecasting model and have good results beyond a certain amount of time. Say, a week or two.

Computers in Meteorology

Apparently, Lorenz discovered this effect by mistake. He had made a computer program as part of another research project and made a miniscule error in one of his inputs. He missed a few digits starting in the fourth decimal place, causing an error of 1/10 of a percent or less.

What did it do to the output? When he reran it with the number corrected, the results were substantially different and he had a hard time believing it.

Meta Butterflies

The butterfly effect has grown as a concept to become an encompassing symbol for the significance of seemingly trivial things in all walks of life. Psychology. Finance. Etc. In fact, the analogy may have come from another instance before the butterfly effect in meteorology example mentioned above.

Someone later noted that in "A Sound of Thunder", a 1952 book by Ray Bradbury, someone alters the future by stepping on a butterfly.

This little story is starting to look like a chaos theory on its own. A chaotic system, actually.

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