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Saturday, February 17, 2001

Global warming
could change day’s
length, scientist says

By Helen Altonn

Not only are global temperatures rising, but atmospheric changes are occurring that could cause the planet to rotate faster, altering the day's length by a fraction of a second and altering the strength of jet streams.

This glimpse of the future is presented by Richard Rosen, president-elect of the American Meteorological Association. He said it's based on a global climate model of the ocean and atmosphere developed at the Canadian Center for Climate Modeling.

Rosen is vice president and chief scientist for Atmospheric and Environmental Research Inc., in Lexington, Mass. He gave a seminar at the International Pacific Research Center, University of Hawaii, and talked to the Aloha chapter of the American Meteorological Society.

"There is a little ... understanding to date on how large-scale wind systems, the circulation of the atmosphere, might change in response to global warming."

One measure is the atmosphere's angular momentum, he said. "Westerlies and easterlies are what we measure as velocity. When you measure that by the mass of atmosphere, you get angular momentum."

It changes on time scales from day-to-day to decadal changes, he said. If the globe loses angular momentum from one day to the next, he said, it shows up in the angular momentum of the planet's solid earth. This means the planet will rotate faster and the day's length will change by fractions of a millisecond,he said.

Meteorologists measure changes in the atmosphere's angular momentum by measuring how the winds change, he said. Those measurements, compared with length-of-day changes, show that when the atmosphere speeds up, the solid earth slows down and vice versa, he said.

Rosen is concerned with changes in the jet stream and angular momentum of the atmosphere. He said that according to the Canadian model, the jet stream's strength will increase tremendously.

If so, he said, tradewinds in the tropics will have "a lot more westerly winds ... and probably lots of other consequences."

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