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Scientists find a big drop in the strength of solar magnetic fields

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Tuesday, June 22, 2010

Although sunspots are making a belated comeback after the protracted solar minimum, the signs are that all is not well. For decades, William Livingston at the National Solar Observatory in Tucson has been measuring the strength of the magnetic fields that puncture the sun's surface and cause the spots to develop. Last year, he and colleague Matt Penn pointed out that the average strength of sunspot magnetic fields has been sliding dramatically since 1995.

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If the trend continues, in just five years the field will have slipped below the threshold needed for sunspots to form. How likely is this to happen? Michael Lockwood, a professor of space environment physics at the University of Reading in England, has scoured historical data for similar periods of solar inactivity, signs of which show up as increases in the occurrence of certain isotopes in ice cores and tree rings. He found 24 such instances in the last few thousand years. On two of those occasions, sunspots all but disappeared for decades. Lockwood puts the chance of this happening now at just 8 percent.

On only one occasion did the sunspot number bounce back to record levels. In the majority of cases, the sun continued producing spots albeit at significantly depressed levels. It seems that the sunspot bonanza of the last century is over.

-- Stuart Clark


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