Wednesday, May 16, 2012

It doesn't take a tornado

kw: winds

I was recently told that on at least two occasions wind speeds exceeding 200 mph (320 kph or 90 m/s) were recorded for "straight line" winds. In 1934 on Mount Washington in New Hampshire (USA), the speed recorded was 231 mph (372 kph or 103 m/s) and in 1996 at Barrow Island, Australia the speed recorded was 253 mph (408 kph or 113 m/s). I can hardly imagine what such wind gusts would do in a populated area.

I recall one occasion on which I observed (from inside a sturdy brick structure) the effects of wind exceeding 90 mph (145 kph or 40 m/s) on a partially-built housing development. It was in Salt Lake City, Utah in 1959, and I was in seventh grade, at a second-story window of the junior high school I attended. Strong winds from the east blew through the mountain canyons of the Wasatch Mountains. The wind through Mill Creek Canyon was funneled right past the school.

We watched in awe as first the partially-built houses, then even the completed ones, were demolished and blown westward. Nobody thought to make us all take shelter on a lower floor. Teachers, students and administrators all watched the demolition. Later, on the way home—and the wind was still blowing at about half the earlier speed—I saw a flagpole in front of another school that had been right over to the ground. It wasn't uprooted, just bent over near its base, in a long curve.

I look back on the experience as a near miss on my part. Wind power increases as the square of velocity. Going just from 90 to 100 doesn't add 11% to the power, but 23.4%. A 200-mph wind is four times as destructive as one at 100. A little difference in the angle of the wind, plus a bit more velocity, and it could have demolished the school building I was in and hurt or killed a lot of us.

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